Wording in Lisachem 2009.

[iffets12345]

Question 7:
N2(g) + O2(g) => 2NO(g)
The equilibrium constant, K, for this equilibrium is x
In a sealed rigid container the concentration of N2 is 0.5,  O2 is 0.25 and concetration of NO is x

Which of hte following statements about this mixure is correct?

A. The rates of the forward and reverse reactions are equal.
B. The forward reaction is proceeding slower than the reverse reaction.
C. The forward reaction is proceeding faster htan the reverse reaction.
D. The pressure in the container is increasing.

I have the same answer as the solutions for the value of K, which is x , evidently less than the actual K.
Where we differ is that I chose B, and they chose C.
I chose B because I interpreted the question as right at that moment , what was happening was that there was more reactants than products hence a backward reaction was being favoured.
But I think the question meant as a result of this, what was happening was that the forward reaction would proceed to ensure more products were formed and equilibrium would be established.

What do you guys think?

[Whatlol]

Question 7:
N2(g) + O2(g) => 2NO(g)
The equilibrium constant, K, for this equilibrium is x
In a sealed rigid container the concentration of N2 is 0.5,  O2 is 0.25 and concetration of NO is x

Which of hte following statements about this mixure is correct?

A. The rates of the forward and reverse reactions are equal.
B. The forward reaction is proceeding slower than the reverse reaction.
C. The forward reaction is proceeding faster htan the reverse reaction.
D. The pressure in the container is increasing.

I have the same answer as the solutions for the value of K, which is x , evidently less than the actual K.
Where we differ is that I chose B, and they chose C.
I chose B because I interpreted the question as right at that moment , what was happening was that there was more reactants than products hence a backward reaction was being favoured.
But I think the question meant as a result of this, what was happening was that the forward reaction would proceed to ensure more products were formed and equilibrium would be established.

What do you guys think?

if the value of K is less than the actual, the forward reaction must be faster than the reverse reaction, as the system will be increasing the ratio of  the concentration of products to that of reactants, i.e to reach equilibrium there must be more products forming than reactants.

[iffets12345]

erm, so you're saying you interpreting it as : since K is less, what follows is that the forward reaction is faster.
Cause I'm thinking instantaneously.

[Whatlol]

erm, so you're saying you interpreting it as : since K is less, what follows is that the forward reaction is faster.
Cause I'm thinking instantaneously.

yes even right at that moment, the forward reaction will be faster than the reverse , since there is an inbalance in reactants and products.

[iffets12345]

okay, cause sometimes you get questions where its like "what does this indicate" at which you would actually say "less product, more reactant.

[Whatlol]

okay, cause sometimes you get questions where its like "what does this indicate" at which you would actually say "less product, more reactant.

yea the wording in these can be ambiguous

[iffets12345]

*sinks into depression*
kay thanks for that!

[Whatlol]

*sinks into depression*
kay thanks for that!

no probs, just make sure you dont confuse the presence of more reactants as there being a faster production of reactants, always think back to le chatelier's principle and what will happen to the equilibrium system.

[m@tty]

There was more reactants than products hence a backward reaction was being favoured.

This is not necessarily true.

When determining what the net reaction is, you need to compare the equilibrium constant(K) with the concentration fraction(Q).

It seems to me that your logic here is that the back reaction is going to be favoured as there is a higher concentration of products compared to reactants, and thus it must back-react till the concentrations are even. This is almost never true. It is entirely dependent on the K value and where the reaction is compared to this.

If Q<K, then a net forward-reaction will occur.

If Q>K then a net back-reaction will occur.

EDIT: Reading that sentence again, I think you may have been referring to the fact that since Q<K, that a back-reaction must have occurred to bring it from equilibrium.

I'm not really sure what you mean. Nevertheless, this may be of some help to someone in the vast nothingness that is the internet.

[iffets12345]

There was more reactants than products hence a backward reaction was being favoured.

EDIT: Reading that sentence again, I think you may have been referring to the fact that since Q<K, that a back-reaction must have occurred to bring it from equilibrium.

Yea that's what I mean. I was thinking "at that instant
 where as if you see what you and Whatlol describe, you use the words "will occur"
So I guess I shall have to think interms of cause and effect now.

[m@tty]

Ok.

There is no indication that the mixture was at equilibrium initially. Actually, it is impossible that it was.

The reaction always proceeds such that Q gets closer to K.

Whenever a change is instigated, the mixture reacts to work its way back to K immediately.

That is the best of my understanding anyway.

[vexx]

iffets- just did this paper actually, and i did the same thing as you, thought it meant at that moment.
i'm sure vcaa wouldn't let that happen.. besides, a few other of the q's in that 09 lisachem have errors - not the best paper, the multichoice was off i reckon.

[akira88]

iffets- just did this paper actually, and i did the same thing as you, thought it meant at that moment.
i'm sure vcaa wouldn't let that happen.. besides, a few other of the q's in that 09 lisachem have errors - not the best paper, the multichoice was off i reckon.

Lol happened to me too. Had a few tricks, but they weren't too unreasonable.

[iffets12345]

iffets- just did this paper actually, and i did the same thing as you, thought it meant at that moment.
i'm sure vcaa wouldn't let that happen.. besides, a few other of the q's in that 09 lisachem have errors - not the best paper, the multichoice was off i reckon.

Literally slapped myself at the enthalpy questino where it was less than double cause of water being in gaseous form.
And yea I think the short answer question where they ask you for the equation between X, Y, Z is a bit weird, the solutions I mean.

Thanks for that.

[tram]

lisachem 2010 had a few dogily worded questiosn as well......