giving

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respond to compliments

BBC Learning English
How to …
respond to compliments
How to … © BBC Learning English 2007
respond to compliments Page 1 of 4
bbclearningenglish.com
William: Hello, and welcome to How to… our guide to the everyday language of life.
My name’s William Kremer. I take every opportunity to shock my colleagues
here at BBC Learning English dot com and earlier on I gave several of them a
big shock. I went around the office complimenting them.
Why did I compliment them? Did they look good? Had they made programmes
that I’d enjoyed? Well no, not really. I just wanted to see how they would react
- how they would respond - to my compliments.
I started off by approaching Carrie at the photocopier. How did she react when
I gave her a compliment?
William: Hello Carrie. You’re looking lovely today…
Carrie: What are you after?
William: What do you mean, what am I after? I’m just saying you look lovely. I like
your purple T-shirt.
Carrie: It’s just you don’t ever normally give me compliments so you must be after
something…
William: Well, I told you that my colleagues would be shocked by me paying them
compliments. When I told Carrie that I thought she looked lovely she said:
‘What are you after?’
William: Hello Carrie. You’re looking lovely today…
Carrie: What are you after?
How to … © BBC Learning English 2007
respond to compliments Page 2 of 4
bbclearningenglish.com
William: ‘What are you after?’ means ‘What do you want?’. Carrie thinks that I am
being nice to her because I want to ask her a favour. She said that I didn’t
normally compliment her so ‘I must be after something’. ‘What are you after?’
is a humorous, and quite common response to an unexpected compliment. It is
sometimes said that the British don’t know how to respond to compliments. So
after Carrie’s rather disappointing answer, I thought I’d try someone from
abroad, so I approached my colleague Khalid….
William: Khalid!
Khalid: Hello!
William: Khalid’s busy. But I just wanted to say… erm you’re looking fantastic today.
As always, actually! You’re so smart….
Khalid: Oh thank you! What do you want?
William: You’re the second person that’s said that! No, I don’t want anything, I don’t
need you to translate anything at all… I just thought I… I… I thought you look
very smart.
Khalid: Well thank you so much, that’s very, very kind. I got my shirt from er Dubai
actually – erm, very cheap shop in Dubai… erm – it didn’t cost me a lot of
money but I think it’s nice, and you think it’s nice.
William: Well, either I don’t ever pay people compliments or my colleagues never
receive any! Khalid also asked me if I wanted anything – if I was looking for a
favour. But then he said, ‘Thank you so much, that’s very kind’.
William: … I just thought I… I… I thought you look very smart.
Khalid: Well thank you so much, that’s very, very kind. I got my shirt from er Dubai
actually – erm, very cheap shop in Dubai… erm – it didn’t cost me a lot of
money but I think it’s nice, and you think it’s nice.
How to … © BBC Learning English 2007
respond to compliments Page 3 of 4
bbclearningenglish.com
William: After Khalid thanked me for the compliment, he went on to tell me about his
shirt – specifically that it hadn’t cost much money. In Britain this is quite a
common way of responding to compliments about clothes – to say that actually
your clothes aren’t so special. We often say ‘Ooh, it was only cheap’ or maybe
‘I’ve had it for ages’. You’re not disagreeing with the compliment, but saying
this kind of thing shows that you’re surprised by it.
Next, I complimented Callum Robertson on his programme Grammar
Challenge, and he replied using a standard phrase.
William: So, I listened to one of your grammar challenges the other day… and erm… I
thought it was fantastic
Callum: Ah well, it’s very nice of you to say so, thanks
William: Callum said ‘It’s very nice of you to say so’
Callum: Ah well, it’s very nice of you to say so, thanks
William: Now, there’s an important strategy that people use in reacting to compliments.
That is to return the compliment – to give a compliment back to the person
who gave it to you! Listen to my conversation with Hina:
William: No, I … I… thought that I’d, I’d come over and compliment you on the way
you’re looking today because I think you’re looking very smart…
Hina: Thank you Will, that’s very kind of you to say. You’re looking very smart and
tall as usual….
William: I’m tall! Yes – I can’t help, I’m always looking tall, that’s just the way I am!
How to … © BBC Learning English 2007
respond to compliments Page 4 of 4
bbclearningenglish.com
William: Hina returned my compliment by saying that I was looking very tall. Normally,
we don’t say that people look tall, we say that they are tall… that’s why I told
Hina that I’m always looking tall.
Hina: You’re looking very smart and tall as usual….
William: I’m tall! Yes – I can’t help, I’m always looking tall, that’s just the way I am!
I am actually a very tall person, and I get a lot of compliments about my height.
Old ladies are always saying to me ‘Oh, you’re lovely and tall’. That sounds
very nice, but actually it gets pretty boring. And, it can be quite difficult for me
to return the compliment. It would be very strange for me to say ‘Oh, thank
you very much. You’re lovely and short’!
But, after someone compliments you, you always need to say something.
Goodbye!

Argument

Argument

An argument is a connected series of statements or propositions, some of which are intended to provide support, justification or evidence for the truth of another statement or proposition. Arguments consist of one or more premises and a conclusion. The premises are those statements that are taken to provide the support or evidence; the conclusion is that which the premises allegedly support. For example, the following is an argument:

The death penalty should be adopted only if it deters murder. However, it could only do this if murderers understood the consequences of their actions before acting, and since this is not so, we must reject adopting the death penalty.

The conclusion of this argument is the final statement: “we must reject reject adopting the death penalty.” The other statements are the premises; they are offered as reasons or justification for this claim. The premises of an argument are sometimes also called the “data,” the “grounds” or the “backup” given for accepting the conclusion.

Because arguments are attempts to provide evidence or support for a certain claim, they often contain words such as “therefore,” “thus,” “hence,” “consequently,” or “so” before their conclusions. Similarly, words or expressions such as “because,” “inasmuch as,” “since,” “for the reason that,” etc., are often found accompanying the premises of an argument. Such “indicators” can aid in the task of identifying the conclusion of the argument, which often comes last in the series of statements making up the argument, as in the example above, but can also come first, or even in the middle, such as in these examples:

Councilwoman Radcliffe is the best person for the job. This is because she has the most legislative experience of all the candidates, and she will not place the interests of corporations above those of the people.

Callisto orbits Jupiter. Hence, it is not a planet, because something must orbit a star in order to be a planet.

In the examples above, the italicized statements are the conclusions. The other statements are offered as reasons or justifications for these claims.

In everyday life, we often use the word “argument” to mean a verbal dispute or disagreement. This is not the way this word is usually used in philosophy. However, the two uses are related. Normally, when two people verbally disagree with each other, each person attempts to convince the other that his or her viewpoint is the right one. Unless he or she merely results to name calling or threats, he or she typically presents an argument for his or her position, in the sense described above. In philosophy, “arguments” are those statements a person makes in the attempt to convince someone of something, or present reasons for accepting a given conclusion.

In normal conversation, certain important elements of an argument might be left implicit or unstated. In the last example given above, the person advancing the argument most likely takes it for granted that his or her audience understands that if something orbits Jupiter, then it does not orbit a star. This supposition is a vital part of the evidence or support that the author intends the stated premises to provide for the conclusion. Here, the statement “if something orbits Jupiter, then it does not orbit a star” is operating as an implicit or unstated premise. Therefore, the above argument is best understood as an abbreviated form of the full argument:

Callisto orbits Jupiter. Something must orbit a star in order to be a planet. If something orbits Jupiter, then it does not orbit a star. Therefore, Callisto is not a planet.

Even the conclusion of an argument can be left unstated if it is obvious enough from context that the speaker intends his or her words to provide evidence for a certain proposition. Consider, for instance:

Only children are allowed on the swingset, and Ms. Peabody, you are no child, are you?

Here, the speaker is obviously inviting Ms. Peabody to draw the conclusion that she is not allowed on the swingset.

Normally, a single statement in isolation does not constitute an argument, but simply a declaration or assertion. For example, if a teacher simply announces at the beginning of a class “Councilwoman Radcliffe voted in favor of the tax increase,” she is not arguing for a given conclusion; she simply intends her students to accept her assertion on its own. However, in the right context, a single statement can abbreviate a whole argument if the other implicit pieces of the argument are clear from the context. In a discussion among conservative politicians discussing whom they’d like to see as the next candidate for Senator, where it is agreed by all participants that no one who supports increased taxes is a desirable candidate, someone might implicitly be arguing against Radcliffe’s candidacy with the simple statement, “Councilwoman Radcliffe voted in favor of the tax increase.” When the implicit premise and implicit conclusion are filled in, the argument in its entirety could be stated in this way:

Councilwoman Radcliffe voted in favor of the tax increase. No one who voted in favor of the tax increase is a desirable candidate. Therefore, Councilwoman Radcliffe is not a desirable candidate.

In an argument, the premises are almost always put forth or claimed to provide support for the conclusion; however, the premises do not always actually provide support. If we take as our example the following argument:

The roulette wheel has landed on red the last five spins. Therefore, since black is “due,” the next spin will probably be black.

The person stating this argument probably thinks that the conclusion is justified by the premise, but he or she would be mistaken. The reasoning here is fallacious. The premise could be true without the conclusion being definitely or even probably true. However, this is still an argument, because the premise is at least intended to provide support or evidence for the conclusion, even if it does not.

Logicians study the criteria to be used in evaluating arguments, i.e., the criteria for determining under what conditions a certain set of premises actually guarantees the truth or likely truth of the conclusion.

Arguments are related to inference and reasoning: i.e., the psychological process through which a person forms a new belief on the basis other beliefs. A course of reasoning can usually be recast or reconstructed as an argument. For example, if someone already believed that all Romance languages were derived from Latin, and then learned that Rumanian was a Romance language, she or he would likely form the new belief that Rumanian was derived from Latin. If this person were to express her or his train of thought out loud or write it down, it would take the form of this argument:

All Romance Languages are derived from Latin. Rumanian is a Romance Language. Therefore, Rumanian is derived from Latin.

However, it should not be thought that the psychological process of inference or the nature of cognition are relevant to the evaluation of arguments. Regardless of whether or not the argument above corresponds to anyone’s psychological process or cognitive behavior, it can be analyed by logicians as valid, because the premises do provide support for the conclusion.

Arguments must be separated off from other uses of language, such as to explain something, give an example, or tell a story. In these cases, one might find a connected series of statements, but the author or speaker does not intend it to be the case that some of them provide support or evidence in favor of one of the others. So they are not arguments. Consequently, one must distinguish arguments fromreports of arguments. If a newspaper journalist includes in her article a description of an argument given by Senator Feingold in favor of campaign finance reform, the reporter is not herself arguing in favor of campaign finance reform nor anything else. She is merely making a report.

There are other uses of language that may appear at first blush to be arguments, but are not. Such is the case with explanations. Sometimes it is agreed by participants in a conversation that a certain event has taken place, or that a certain thing is true. Suppose, for example, it is agreed that Alex is late for his job. Someone might explain this fact as follows:

Alex’s car broke down yesterday, and without it he cannot get to work on time. Therefore, he is late for work today.

The above may appear to be an argument. In fact, it has the same structure as an argument, and even includes the indicator “therefore.” However, notice that the person speaking these words is not attempting to provide support or evidence for the truth of the claim that “Alex is late for work today:” that is already accepted as true in this context by everyone involved. Properly speaking, the above example is an explanation, not an argument. However, in another context, in which it was not generally known that Alex is late for work today, these very words could be used as an argument. Consequently, it is impossible to ascertain whether or not a certain utterance is an argument without ascertaining the speaker’s intentions within the given context. (For more on the relationship between arguments and explanation, see the article on “Scientific Explanation.”)

Much of philosophy consists in the evaluation of particular arguments, some simple, some complicated. Descartes’s famous three word saying, “cogito ergo sum” (I think, therefore I am) represents an extremely compact argument, with a single premise, that he is thinking, to the conclusion that he exists. Other philosophical arguments are more complicated and elaborate. Consider the following argument from Plato’s Apology:

Let us reflect in another way, and we shall see that there is great reason to hope that death is a good, for one of two things: — either death is a state of nothingness and utter unconsciousness, or, as men say, there is a change and migration of the soul from this world to another. Now if you suppose that there is no consciousness, but a sleep like the sleep of him who is undisturbed even by the sight of dreams, death will be an unspeakable gain. For if a person were to select the night in which his sleep was undisturbed even by dreams, and were to compare with this the other days and nights of his life, and then were to tell us how many days and nights he had passed in the course of his life better and more pleasantly than this one, I think that any man, I will not say a private man, but even the great king, will not find many such days or nights, when compared with the others. Now if death is like this, I say that to die is gain; for eternity is then only a single night. But if death is the journey to another place, and there, as men say, all the dead are, what good, O my friends and judges, can be greater than this? If indeed when the pilgrim arrives in the world below, he is delivered from the professors of justice in this world, and finds the true judges who are said to give judgment there, Minos and Rhadamanthus and Aeacus and Triptolemus, and other sons of God who were righteous in their own life, that pilgrimage will be worth making. What would not a man give if he might converse with Orpheus and Musaeus and Hesiod and Homer? Nay, if this be true, let me die again and again.

Here the character Socrates argues for the conclusion that death is a good. The justification he offers for the conclusion, however, is rather elaborate; he offers quite a few premises, which, taken together, are thought to provide support for the conclusion.

Note: There is another, completely distinct, use of the word “argument,” that can also be relevant to logic, specifically, to the logic of functions and relations. An argument to a function is contrasted with the value of that function. Loosely speaking, the argument is the input, the value is the output. When the square root function takes 9 “as argument,” the value is 3. When it takes 16 “as argument,” the value is 4. Different functions take a different number of arguments. The square root function takes a single argument; whereas addition and multiplication require two arguments to yield a value. I.e., in the equation, x + y = z, x and y are the arguments to the addition function, and z is the value. Sometimes, logicians also speak of predicates and relations as having a certain number of “argument-places.” For example, the relation expression “___ is taller than …” is said to have two argument places, because it requires completion by two terms to form a complete proposition.

See also the articles on Deductive and Inductive Arguments, Validity and Soundness, Propositional Logic, and Fallacies in this encyclopedia.
Author Information

The author of this article is anonymous. The IEP is actively seeking an author who will write a replacement article.

Agreement/Disagreement

Agreement/Disagreement

See Also: COMPATIBILITY, FIGHTING

1. About as far apart as an atheist and a born-again Christian —Anon
2. Acquiesced like an old man acquiescing in death —Wilfrid Sheed
3. (Nobody can be as) agreeable as an uninvited guest —Frank McKinney

Humorists like McKinney are notable phrase converters. This simile may be a case in point, evolving from William Wordsworth’s sonnet To a Snowdrop which describes a flower bending its forehead “As if fearful to offend, like an unbidden guest.”

See Also: BEHAVIOR
4. Agree like a finger and a thumb —Anon
5. Agree like two cats in a gutter —John Heywood’s Proverbs
6. Agree like cats and dogs —John Ray’s Proverbs

This sarcastic twist to the more commonly used “Fight like cats and dogs” dates back to the nineteenth century.
7. Agree like pickpockets in a fair —John Ray’s Proverbs
8. Agree like the clocks of London —Richard Brinsley Sheridan
9. As coals are to burning coals, and wood to fire, so is a contentious man to kindle strife —The Holy Bible/Proverbs
10. As far apart as the atheists who claim there is no soul, and the Christian Scientists who declare there is no body —Anon
11. Co-operate about as much as two tomcats on a fence —Raymond Chandler
12. Far apart as the poles —Anon
13. Flock together in consent, like so many wild geese —William Shakespeare
14. Like the course of the heavenly bodies, harmony in national life is a resultant of the struggle between contending forces —Judge Louis D. Brandeis
15. Sentiments as equal as if weighed on a golden scale —Janet Flanner
16. We are made for cooperation, like feet, like hands, like eyelids, like the row of the upper and lower teeth. To act against one another is contrary to nature —Marcus Aurelius

Agreement

Subject-Verb
Agreement
#
PowerpointIf your computer is equipped with PowerPoint, click on the PowerPoint icon to the right for a brief PowerPoint presentation on Subject-Verb Agreement.
Click HERE for help with Powerpoint.

Basic Principle: Singular subjects need singular verbs; plural subjects need plural verbs. My brother is a nutritionist. My sisters are mathematicians.

See the section on Plurals for additional help with subject-verb agreement.

1

The indefinite pronouns anyone, everyone, someone, no one, nobody are always singular and, therefore, require singular verbs.

* Everyone has done his or her homework.
* Somebody has left her purse.

Some indefinite pronouns — such as all, some — are singular or plural depending on what they're referring to. (Is the thing referred to countable or not?) Be careful choosing a verb to accompany such pronouns.

* Some of the beads are missing.
* Some of the water is gone.

On the other hand, there is one indefinite pronoun, none, that can be either singular or plural; it often doesn't matter whether you use a singular or a plural verb — unless something else in the sentence determines its number. (Writers generally think of none as meaning not any and will choose a plural verb, as in "None of the engines are working," but when something else makes us regard none as meaning not one, we want a singular verb, as in "None of the food is fresh.")

* None of you claims responsibility for this incident?
* None of you claim responsibility for this incident?
* None of the students have done their homework. (In this last example, the word their precludes the use of the singular verb.


2

Some indefinite pronouns are particularly troublesome Everyone and everybody (listed above, also) certainly feel like more than one person and, therefore, students are sometimes tempted to use a plural verb with them. They are always singular, though. Each is often followed by a prepositional phrase ending in a plural word (Each of the cars), thus confusing the verb choice. Each, too, is always singular and requires a singular verb.

Everyone has finished his or her homework.

You would always say, "Everybody is here." This means that the word is singular and nothing will change that.

Each of the students is responsible for doing his or her work in the library.

Don't let the word "students" confuse you; the subject is each and each is always singular — Each is responsible.
3

Phrases such as together with, as well as, and along with are not the same as and. The phrase introduced by as well as or along with will modify the earlier word (mayor in this case), but it does not compound the subjects (as the word and would do).

* The mayor as well as his brothers is going to prison.
* The mayor and his brothers are going to jail.

4

The pronouns neither and either are singular and require singular verbs even though they seem to be referring, in a sense, to two things.

* Neither of the two traffic lights is working.
* Which shirt do you want for Christmas?
Either is fine with me.

In informal writing, neither and either sometimes take a plural verb when these pronouns are followed by a prepositional phrase beginning with of. This is particularly true of interrogative constructions: "Have either of you two clowns read the assignment?" "Are either of you taking this seriously?" Burchfield calls this "a clash between notional and actual agreement."*
5

The conjunction or does not conjoin (as and does): when nor or or is used the subject closer to the verb determines the number of the verb. Whether the subject comes before or after the verb doesn't matter; the proximity determines the number.

* Either my father or my brothers are going to sell the house.
* Neither my brothers nor my father is going to sell the house.
* Are either my brothers or my father responsible?
* Is either my father or my brothers responsible?

Because a sentence like "Neither my brothers nor my father is going to sell the house" sounds peculiar, it is probably a good idea to put the plural subject closer to the verb whenever that is possible.
6

The words there and here are never subjects.

* There are two reasons [plural subject] for this.
* There is no reason for this.
* Here are two apples.

With these constructions (called expletive constructions), the subject follows the verb but still determines the number of the verb.
7

Verbs in the present tense for third-person, singular subjects (he, she, it and anything those words can stand for) have s-endings. Other verbs do not add s-endings.

He loves and she loves and they love_ and . . . .

8

Sometimes modifiers will get betwen a subject and its verb, but these modifiers must not confuse the agreement between the subject and its verb.

The mayor, who has been convicted along with his four brothers on four counts of various crimes but who also seems, like a cat, to have several political lives, is finally going to jail.

9

Sometimes nouns take weird forms and can fool us into thinking they're plural when they're really singular and vice-versa. Consult the section on the Plural Forms of Nouns and the section on Collective Nouns for additional help. Words such as glasses, pants, pliers, and scissors are regarded as plural (and require plural verbs) unless they're preceded the phrase pair of (in which case the word pair becomes the subject).

* My glasses were on the bed.
* My pants were torn.
* A pair of plaid trousers is in the closet.

10

Some words end in -s and appear to be plural but are really singular and require singular verbs.

* The news from the front is bad.
* Measles is a dangerous disease for pregnant women.

On the other hand, some words ending in -s refer to a single thing but are nonetheless plural and require a plural verb.

* My assets were wiped out in the depression.
* The average worker's earnings have gone up dramatically.
* Our thanks go to the workers who supported the union.

The names of sports teams that do not end in "s" will take a plural verb: the Miami Heat have been looking … , The Connecticut Sun are hoping that new talent … . See the section on plurals for help with this problem.
11

Fractional expressions such as half of, a part of, a percentage of, a majority of are sometimes singular and sometimes plural, depending on the meaning. (The same is true, of course, when all, any, more, most and some act as subjects.) Sums and products of mathematical processes are expressed as singular and require singular verbs. The expression "more than one" (oddly enough) takes a singular verb: "More than one student has tried this."

* Some of the voters are still angry.
* A large percentage of the older population is voting against her.
* Two-fifths of the troops were lost in the battle.
* Two-fifths of the vineyard was destroyed by fire.
* Forty percent of the students are in favor of changing the policy.
* Forty percent of the student body is in favor of changing the policy.
* Two and two is four.
* Four times four divided by two is eight.

12

If your sentence compounds a positive and a negative subject and one is plural, the other singular, the verb should agree with the positive subject.

* The department members but not the chair have decided not to teach on Valentine's Day.
* It is not the faculty members but the president who decides this issue.
* It was the speaker, not his ideas, that has provoked the students to riot.

For additional help with subject-verb agreement, see Chapter 12 of Sentence Sense: A Writer's Guide.

Expressing Opinions

Expressing Opinions
English Vocabulary

Below are some phrases that you can use to help express opinions. Some of these phrases are more appropriate for written English such as giving your opinion in an essay whereas some can also be used in spoken English.

Personal Point of View

We use these words and phrases to express a personal point of view:

* In my experience…
* As far as I’m concerned…
* Speaking for myself…
* In my opinion…
* Personally, I think…
* I’d say that…
* I’d suggest that…
* I’d like to point out that…
* I believe that…
* What I mean is…


General Point of View

We use these words and phrases to express a point of view that is generally thought by people:

* It is thought that...
* Some people say that...
* It is considered...
* It is generally accepted that...


Agreeing with an opinion

We use these words and phrases to agree with someone else’s point of view:

* Of course.
* You’re absolutely right.
* Yes, I agree.
* I think so too.
* That’s a good point.
* Exactly.
* I don’t think so either.
* So do I.
* I'd go along with that.
* That’s true.
* Neither do I.
* I agree with you entirely.
* That's just what I was thinking.
* I couldn't agree more.


Disagreeing with an opinion

We use these words and phrases to disagree with someone else’s point of view:

* That’s different.
* I don’t agree with you.
* However…
* That’s not entirely true.
* On the contrary…
* I’m sorry to disagree with you, but…
* Yes, but don’t you think…
* That’s not the same thing at all.
* I’m afraid I have to disagree.
* I'm not so sure about that.
* I must take issue with you on that.
* It's unjustifiable to say that...

kesetimbangan kimia

Kesetimbangan kimia

Reaksi yang dapat berlangsung dalam dua arah disebut reaksi dapat balik. Apabila dalam suatu reaksi kimia, kecepatan reaksi ke kanan sama dengan kecepatan reaksi ke kiri maka, reaksi dikatakan dalam keadaan setimbang. Secara umum reaksi kesetimbangan dapat dinyatakan sebagai:
A + B ® C + D

ADA DUA MACAM SISTEM KESETIMBANGAN, YAITU :
1.

Kesetimbangan dalam sistem homogen
a.

Kesetimbangan dalam sistem gas-gas
Contoh: 2SO2(g) + O2(g) « 2SO3(g)
b.

Kesetimbangan dalam sistem larutan-larutan
Contoh: NH4OH(aq) « NH4+(aq) + OH- (aq)
2.

Kesetimbangan dalam sistem heterogen
a.

Kesetimbangan dalam sistem padat gas
Contoh: CaCO3(s) « CaO(s) + CO2(g)
b.

Kesetimbangan sistem padat larutan
Contoh: BaSO4(s) « Ba2+(aq) + SO42- (aq)
c.

Kesetimbangan dalam sistem larutan padat gas
Contoh: Ca(HCO3)2(aq) « CaCO3(s) + H2O(l) + CO2(g)


Hukum Guldberg dan Wange:

Dalam keadaan kesetimbangan pada suhu tetap, maka hasil kali konsentrasi zat-zat hasil reaksi dibagi dengan hasil kali konsentrasi pereaksi yang sisa dimana masing-masing konsentrasi itu dipangkatkan dengan koefisien reaksinya adalah tetap.
Pernyataan tersebut juga dikenal sebagai hukum kesetimbangan.
Untuk reaksi kesetimbangan: a A + b B « c C + d D maka:
Kc = (C)c x (D)d / (A)a x (B)b

Kc adalah konstanta kesetimbangan yang harganya tetap selama suhu tetap.
BEBERAPA HAL YANG HARUS DIPERHATIKAN
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Jika zat-zat terdapat dalam kesetimbangan berbentuk padat dan gas yang dimasukkan dalam, persamaan kesetimbangan hanya zat-zat yang berbentuk gas saja sebab konsentrasi zat padat adalah tetap den nilainya telah terhitung dalam harga Kc itu.
Contoh: C(s) + CO2(g) « 2CO(g)
Kc = (CO)2 / (CO2)
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Jika kesetimbangan antara zat padat dan larutan yang dimasukkan dalam perhitungan Kc hanya konsentrasi zat-zat yang larut saja.
Contoh: Zn(s) + Cu2+(aq) « Zn2+(aq) + Cu(s)
Kc = (Zn2+) / (CO2+)
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Untuk kesetimbangan antara zat-zat dalam larutan jika pelarutnya tergolong salah satu reaktan atau hasil reaksinya maka konsentrasi dari pelarut itu tidak dimasukkan dalam perhitungan Kc.
Contoh: CH3COO-(aq) + H2O(l) « CH3COOH(aq) + OH-(aq)
Kc = (CH3COOH) x (OH-) / (CH3COO-)

Contoh soal:
1. Satu mol AB direaksikan dengan satu mol CD menurut persamaan reaksi:
AB(g) + CD(g) « AD(g) + BC(g)
Setelah kesetimbangan tercapai ternyata 3/4 mol senyawa CD berubah menjadi AD dan BC. Kalau volume ruangan 1 liter, tentukan tetapan kesetimbangan untuk reaksi ini !
Jawab:
Perhatikan reaksi kesetimbangan di atas jika ternyata CD berubah (bereaksi) sebanyak 3/4 mol maka AB yang bereaksi juga 3/4 mol (karena koefsiennya sama).
Dalam keadaan kesetimbangan:
(AD) = (BC) = 3/4 mol/l
(AB) sisa = (CD) sisa = 1 - 3/4 = 1/4 n mol/l
Kc = [(AD) x (BC)]/[(AB) x (CD)] = [(3/4) x (3/4)]/[(1/4) x (1/4)] = 9
2. Jika tetapan kesetimbangan untuk reaksi:
A(g) + 2B(g) « 4C(g)
sama dengan 0.25, maka berapakah besarnya tetapan kesetimbangan bagi reaksi:
2C(g) « 1/2A(g) + B(g)
Jawab:
- Untuk reaksi pertama: K1 = (C)4/[(A) x (B)2] = 0.25
- Untuk reaksi kedua : K2 = [(A)1/2 x (B)]/(C)2
- Hubungan antara K1 dan K2 dapat dinyatakan sebagai:
K1 = 1 / (K2)2 ® K2 = 2
Azas Le Chatelier menyatakan: Bila pada sistem kesetimbangan diadakan aksi, maka sistem akan mengadakan reaksi sedemikian rupa sehingga pengaruh aksi itu menjadi sekecil-kecilnya.
Perubahan dari keadaan kesetimbangan semula ke keadaan kesetimbangan yang baru akibat adanya aksi atau pengaruh dari luar itu dikenal dengan pergeseran kesetimbangan.
Bagi reaksi:
A + B « C + D

KEMUNGKINAN TERJADINYA PERGESERAN
1.

Dari kiri ke kanan, berarti A bereaksi dengan B memhentuk C dan D, sehingga jumlah mol A dan Bherkurang, sedangkan C dan D bertambah.
2.

Dari kanan ke kiri, berarti C dan D bereaksi membentuk A dan B. sehingga jumlah mol C dan Dherkurang, sedangkan A dan B bertambah.

FAKTOR-FAKTOR YANG DAPAT MENGGESER LETAK KESETIMBANGAN ADALAH :
a. Perubahan konsentrasi salah satu zat
b. Perubahan volume atau tekanan
c. Perubahan suhu
A. PERUBAHAN KONSENTRASI SALAH SATU ZAT
Apabila dalam sistem kesetimbangan homogen, konsentrasi salah satu zat diperbesar, maka kesetimbangan akan bergeser ke arah yang berlawanan dari zat tersebut. Sebaliknya, jika konsentrasi salah satu zat diperkecil, maka kesetimbangan akan bergeser ke pihak zat tersebut.
Contoh: 2SO2(g) + O2(g) « 2SO3(g)
- Bila pada sistem kesetimbangan ini ditambahkan gas SO2, maka kesetimbangan akan bergeser ke kanan.
- Bila pada sistem kesetimbangan ini dikurangi gas O2, maka kesetimbangan akan bergeser ke kiri.
B. PERUBAHAN VOLUME ATAU TEKANAN
Jika dalam suatu sistem kesetimbangan dilakukan aksi yang menyebabkan perubahan volume (bersamaan dengan perubahan tekanan), maka dalam sistem akan mengadakan berupa pergeseran kesetimbangan.
Jika tekanan diperbesar = volume diperkecil, kesetimbangan akan bergeser ke arah jumlah Koefisien Reaksi Kecil.
Jika tekanan diperkecil = volume diperbesar, kesetimbangan akan bergeser ke arah jumlah Koefisien reaksi besar.
Pada sistem kesetimbangan dimana jumlah koefisien reaksi sebelah kiri = jumlah koefisien sebelah kanan, maka perubahan tekanan/volume tidak menggeser letak kesetimbangan.
Contoh:
N2(g) + 3H2(g) « 2NH3(g)

Koefisien reaksi di kanan = 2
Koefisien reaksi di kiri = 4
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Bila pada sistem kesetimbangan tekanan diperbesar (= volume diperkecil), maka kesetimbangan akan
bergeser ke kanan.
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Bila pada sistem kesetimbangan tekanan diperkecil (= volume diperbesar), maka kesetimbangan akan
bergeser ke kiri.

C. PERUBAHAN SUHU

Menurut Van't Hoff:
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Bila pada sistem kesetimbangan subu dinaikkan, maka kesetimbangan reaksi akan bergeser ke arah yang membutuhkan kalor (ke arah reaksi endoterm).
-

Bila pada sistem kesetimbangan suhu diturunkan, maka kesetimbangan reaksi akan bergeser ke arah yang membebaskan kalor (ke arah reaksi eksoterm).
Contoh:
2NO(g) + O2(g) « 2NO2(g) ; DH = -216 kJ
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Jika suhu dinaikkan, maka kesetimbangan akan bergeser ke kiri.
-

Jika suhu diturunkan, maka kesetimbangan akan bergeser ke kanan.
PENGARUH KATALISATOR TERHADAP KESETIMBANGAN
Fungsi katalisator dalam reaksi kesetimbangan adalah mempercepat tercapainya kesetimbangan dan tidak merubah letak kesetimbangan (harga tetapan kesetimbangan Kc tetap), hal ini disebabkan katalisator mempercepat reaksi ke kanan dan ke kiri sama besar.

HUBUNGAN ANTARA HARGA Kc DENGAN Kp

Untuk reaksi umum:

a A(g) + b B(g) « c C(g) + d D(g)

Harga tetapan kesetimbangan:
Kc = [(C)c . (D)d] / [(A)a . (B)b]
Kp = (PCc x PDd) / (PAa x PBb)
dimana: PA, PB, PC dan PD merupakan tekanan parsial masing-masing gas A, B. C dan D.

Secara matematis, hubungan antara Kc dan Kp dapat diturunkan sebagai:
Kp = Kc (RT) Dn
dimana Dn adalah selisih (jumlah koefisien gas kanan) dan (jumlah koefisien gas kiri).
Contoh:
Jika diketahui reaksi kesetimbangan:
CO2(g) + C(s) « 2CO(g)

Pada suhu 300o C, harga Kp= 16. Hitunglah tekanan parsial CO2, jika tekanan total dalaun ruang 5 atm!
Jawab:
Misalkan tekanan parsial gas CO = x atm, maka tekanan parsial gas CO2 = (5 - x) atm.
Kp = (PCO)2 / PCO2 = x2 / (5 - x) = 16 ® x = 4
Jadi tekanan parsial gas CO2 = (5 - 4) = 1 atm
Disosiasi adalah penguraian suatu zat menjadi beberapa zat lain yang lebih sederhana.
Derajat disosiasi adalah perbandingan antara jumlah mol yang terurai dengan jumlah mol mula-mula.
Contoh:
2NH3(g) « N2(g) + 3H2(g)
besarnya nilai derajat disosiasi (a):
a = mol NH3 yang terurai / mol NH3 mula-mula

Harga derajat disosiasi terletak antara 0 dan 1, jika:
a = 0 berarti tidak terjadi penguraian
a = 1 berarti terjadi penguraian sempurna
0 < a < 1 berarti disosiasi pada reaksi setimbang (disosiasi sebagian).
Contoh:
Dalam reaksi disosiasi N2O4 berdasarkan persamaan

N2O4(g) « 2NO2(g)

banyaknya mol N2O4 dan NO2 pada keadaan setimbang adalah sama.
Pada keadaan ini berapakah harga derajat disosiasinya ?
Jawab:
Misalkan mol N2O4 mula-mula = a mol
mol N2O4 yang terurai = a a mol ® mol N2O4 sisa = a (1 - a) mol
mol NO2 yang terbentuk = 2 x mol N2O4 yang terurai = 2 a a mol
Pada keadaan setimbang:
mol N2O4 sisa = mol NO2 yang terbentuk
a(1 - a) = 2a a ® 1 - a = 2 a ® a = 1/3