KBT Exam Queries

[Nobby]

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[charmanderp]

How do you work out the first one without knowing how much C and D you have initially? It's easy enough to work out how much is produced from the reaction between A and B but in order to work out equilibrium concentrations you need to be able to tell how much is present at equilibrium, including how much was present before the reaction started!

Question 7 is flawed imo, unless we work under the assumption that all of the C and D present at equilibrium has come from A and B, which contradicts the first line where it says 'all four substances are dissolved'. If we did work under that assumption only (A) would be correct though.

For the second one both carbon dioxide and methane would be appropriate, I think.

[Nobby]

How do you work out the first one without knowing how much C and D you have initially? It's easy enough to work out how much is produced from the reaction between A and B but in order to work out equilibrium concentrations you need to be able to tell how much is present at equilibrium, including how much was present before the reaction started!

Question 7 is flawed imo, unless we work under the assumption that all of the C and D present at equilibrium has come from A and B, which contradicts the first line where it says 'all four substances are dissolved'. If we did work under that assumption only (A) would be correct though.

The reaction begins with just 1.00 mol of A and
0.50 mol of B present.

I think we just assume that these are the initial conditions.

I was thinking both A and D would be correct, because if the coefficient for D was 2 as in answer A, [D] = 0.50 M, so D² = 0.25.
But if the coefficient of D is 1 as in answer D, [D] = 0.25, and has effectively the same effect on the concentration fraction.
But

[charmanderp]

Oooh right, didn't see the word 'just'. My bad. I'll take another look at it soon.

[thushan]

A and D are both right.