Am I going crazy or are these answer wrong?

[Geoo]

So here are some questions with the answer given, and I do think that they are wrong.

So for question 9, it is asking my what would improve the yield of the product.
So, this would be options I and III. There are technically no choices for this, so I pick A as the closest option.

For question 10, I also pick A, as there will be no change in the equilibrium position if the volume is decreased, as there is a 2:2 ratio of particles in the equation. Plus all the other answers appear wrong, and the suggested answer D states it will favour the forward, even though it won't.....
Here are the "correct answers"


Am I missing something here? I feel like the answers are contradicting themselves...

[sweetcheeks]

Where are these questions from? Is the answer key the correct one for the exam? The answers definitely don't match the questions. For Q9, I and III is not a listed option. For Q10, the answer seems like it is written for a similar type of question but definitely not that one.

I've sometimes found with non VCAA exams (and sometimes even with VCAA exams) there can be some pretty serious mistakes, so you always need to be vigilant about answers to questions (even if the answer you get matches theirs). Sometimes they may be reusing many old questions and slightly modifying them, but forget to update them in the answer key.

I also have a gripe with answers that only show working out by process of elimination, like with Q9. It's okay to eliminate wrong answers, but at the same time, you need to have an understanding of why the answer you've selected is correct. You don't really learn anything by being told that an answer is correct because the other options are wrong.

[whys]

Question 9: The answer should be I and III as already said above, this seems to be an error of the book you are working from.

I would like to add that for question 10, the given answer is correct (it should be D). Have a read of this (from my notes):
Changing pressure/volume (with regards to gases only)
   - If pressure decreases, then volume increases (reaction will move to the side that makes the most particles in the products)
   - If pressure increases, then volume decreases (reaction will move to the side that makes the least particles in the products)
Changing pressure by adding inert gas has no effect on Kc (all gases will always have the same partial pressures)

So, when there is a 'sharp decrease in volume', this means the there is a sharp increase in pressure (since volume and pressure are inversely proportional). As a result, the reaction will try to move to the side that produces the least amount of particles (since there is less volume).

The given equation in the question is hydrogen + iodine ---> hydrogen iodide (all gases)
AKA it is in the form:
A + B ---> C
Since the products side has fewer particles than the reactants side, the forward reaction will speed up. The suggested solutions are correct, but the explanations are wrong. You are probably better off referring to the examiners report.

[Geoo]

Question 9: The answer should be I and III as already said above, this seems to be an error of the book you are working from.

I would like to add that for question 10, the given answer is correct (it should be D). Have a read of this (from my notes):
Changing pressure/volume (with regards to gases only)
   - If pressure decreases, then volume increases (reaction will move to the side that makes the most particles in the products)
   - If pressure increases, then volume decreases (reaction will move to the side that makes the least particles in the products)
Changing pressure by adding inert gas has no effect on Kc (all gases will always have the same partial pressures)

So, when there is a 'sharp decrease in volume', this means the there is a sharp increase in pressure (since volume and pressure are inversely proportional). As a result, the reaction will try to move to the side that produces the least amount of particles (since there is less volume).

The given equation in the question is hydrogen + iodine ---> hydrogen iodide (all gases)
AKA it is in the form:
A + B ---> C
Since the products side has fewer particles than the reactants side, the forward reaction will speed up. The suggested solutions are correct, but the explanations are wrong. You are probably better off referring to the examiners report.

You logic is the same as mine but question 9 is still wrong if you use the same theory. Since the pressure has increased due to the decrease in volume, the system will partially oppose this change. To do this, is will favour the side with the least particles. But, if you look at the balanced equation, the are 2 particles on the reactants and 2 particles on the products, using the coefficients.
A + B ---> 2C.
So, since the amount of particles on both side are the same, there should be no compensation for the decrease in volume, as there is a balanced amount of particles on each side. So there would be no change in the forward or backward reaction, hence D would be wrong.

So, option D should still be incorrect?

[whys]

You logic is the same as mine but question 9 is still wrong if you use the same theory. Since the pressure has increased due to the decrease in volume, the system will partially oppose this change. To do this, is will favour the side with the least particles. But, if you look at the balanced equation, the are 2 particles on the reactants and 2 particles on the products, using the coefficients.
A + B ---> 2C.
So, since the amount of particles on both side are the same, there should be no compensation for the decrease in volume, as there is a balanced amount of particles on each side. So there would be no change in the forward or backward reaction, hence D would be wrong.

So, option D should still be incorrect?

I didn't read the coefficients! Hahaha whoops...
Yeah in that case your answer should be right!