Equilibrium questions help

[hpras12]

I have some questions in my homework that i don't understand regarding equilibrium systems.

The first reaction is 2Ag⁺ (aq) + CrO4^2- (aq) <--> Ag2CrO4 (s) where change in enthalpy is negative, and the question is to predict the effect on the concentration of Ag⁺ when equilibrium is re-established after some solid Ag2CrO4 is added to the system.

I thought that adding the solid doesn't have any change in the concentration of Ag⁺ because Ag2CrO4 is a solid and increasing the volume of solid doesn't increases the concentration of the solid. (However the question did say Ag2CrO4 was slightly soluble so i think thats why concentration of Ag⁺ increases).

The second reaction is N2O3 (g) <--> NO (g) + NO2 (g) where change in enthalpy is positive. The question is predict the effect on the concentration of products when equilibrium is re - established when the temperature of the system is decreased.
 
I thought the answer was that the concentration of products decreases because decreasing the temperature will favour the exothermic reaction which in this case is the reverse reaction. So there will be a net reverse reaction causing concentration to decreases. However the answer says it increases.

Final reaction is BaCO3 (s) <--> BaO (s) + CO2 (g) where enthalpy is negative. Predict the effect on the rate of forward reaction when CO2 is removed.

I thought that the forward reaction rate won't change because only reverse reaction rate is decreased (pressure of CO2 is decreased) and that should not affect the forward rate. (Im probably wrong though). The answer claims that there will be an increase in the forward rate.

I know this is a lot i should probably study more. Thanks for any replies

[Bri MT]

I have some questions in my homework that i don't understand regarding equilibrium systems.

The first reaction is 2Ag⁺ (aq) + CrO4^2- (aq) <--> Ag2CrO4 (s) where change in enthalpy is negative, and the question is to predict the effect on the concentration of Ag⁺ when equilibrium is re-established after some solid Ag2CrO4 is added to the system.

I thought that adding the solid doesn't have any change in the concentration of Ag⁺ because Ag2CrO4 is a solid and increasing the volume of solid doesn't increases the concentration of the solid. (However the question did say Ag2CrO4 was slightly soluble so i think thats why concentration of Ag⁺ increases).

Generally, if you have a reversible reaction and you add to one side you can expect to the reaction to favour production of other side. If the solid wasn't soluble at all, we wouldn't have this reaction in the first place - and I don't really think VCAA expects you to worry about the impact that being in a particular state will have for a question like this.

The second reaction is N2O3 (g) <--> NO (g) + NO2 (g) where change in enthalpy is positive. The question is predict the effect on the concentration of products when equilibrium is re - established when the temperature of the system is decreased.
 
I thought the answer was that the concentration of products decreases because decreasing the temperature will favour the exothermic reaction which in this case is the reverse reaction. So there will be a net reverse reaction causing concentration to decreases. However the answer says it increases.

Your reasoning sounds good - where did this question/answer come from?
(They might be trying to argue from a decrease in temp, decrease in pressure perspective? but your answer should be correct)

Final reaction is BaCO3 (s) <--> BaO (s) + CO2 (g) where enthalpy is negative. Predict the effect on the rate of forward reaction when CO2 is removed.

I thought that the forward reaction rate won't change because only reverse reaction rate is decreased (pressure of CO2 is decreased) and that should not affect the forward rate. (Im probably wrong though). The answer claims that there will be an increase in the forward rate.

I know this is a lot i should probably study more. Thanks for any replies

You'd expect both the reverse reaction rate to decrease and the forward reaction rate to increase. For these types of questions, we're looking at yield which is all about the rate of the reactions relative to each other - if one decreases, the opposite increases


No need to beat yourself up about wanting some clarification and not being sure of everything; I didn't know any of this stuff when I was in year 11