1. State whether the given changes will cause the equilibrium to shift toward th
ID: 1002162 • Letter: 1
Question
1. State whether the given changes will cause the equilibrium to shift toward the reactants, products, or neither. Explain each answer.
Ag2CrO4 (s) + heat -> 2Ag+ (aq) + CrO42- (aq)
a. Add more Ag2CrO4 (s)
b. Increase Temperature
c. Add AgNO3 (aq)
d. Increase pressure
e. Add NaCl (aq) (hint: it precipitates AgCl)
2. State whether the given changes will cause the equilibrium to shift toward the reactants, products, or neither. Explain each answer.
BaCO3 (s) + heat -> BaO (s) + CO2 (g)
a. Add BaCO3 (s)
b. increase temperature
c. increase pressure
d. increase volume
e. add CO2 (g)
Explanation / Answer
- State whether the given changes will cause the equilibrium to shift toward the reactants, products, or neither. Explain each answer.
Ag2CrO4 (s) + heat -----> 2Ag+ (aq) + CrO42- (aq)
- Add more Ag2CrO4 (s)
Neither.
The addition of any pure solid, in this case silver chromate, will not have any effect in the reaction equilibrium or the concentration of that compound. Usually the equilibrium can change if the component change its concentration and this is not the case. Add more solid (depending on quantity) will cause this to precipitate without altering the composition of the solution in equilibrium, since by definition this solid is out of solution. It also happen that the number of moles of that compound and the total number of moles of the reaction are going to change by the same factor, so the equilibrium is not affected.
- Increase Temperature
Shift equilibrium to the right (to products).
As we can see this is an endothermic reaction, it means that the reaction needs energy to be carried out. We can know this by the heat applied to the reaction (heat in reactants side). Any endothermic reaction with increased temperature will shift the equilibrium to the right (products) to counteract the change in temperature, this will allow to cool the system.
- Add AgNO3 (aq)
Shift the equilibrium to the left (to reactants).
This is because we are adding a common ion (silver ion), and this will increase the concentration of silver ion on the products side, causing the equilibrium to shift towards the reactants to compensate for the added ion, meaning that less solid will dissolve.
- Increase pressure
Neither.
Since this only applies to reactions involving gases, however not all species need to be in the gas phase.
- Add NaCl (aq) (hint: it precipitates AgCl)
Shift equilibrium to the right (to products).
As a precipitate forms the reaction is favored towards the products. Silver and chlorine form a white precipitate, since they are insoluble.
- State whether the given changes will cause the equilibrium to shift toward the reactants, products, or neither. Explain each answer.
BaCO3 (s) + heat -----> BaO (s) + CO2 (g)
- Add BaCO3 (s)
Neither.
Same explanation of the problem above. Pure solids do not interfere with the equilibrium.
- Increase temperature
Shift equilibrium to the right (to products).
Same explanation of the problem above. This is an endothermic reaction, needing enery to be carried out. So, increasing temperature will shift the equilibrium to the right.
- Increase pressure
Shift equilibrium to the left (to reactants).
Here is different since we have carbon dioxide in a gas phase. The equilibrium will shift to the left since an increase in pressure favors the side that has less number of moles. Here we only see the compounds present in gas phase.
As we can see the left side has zero moles of gas and the right side has 1 mole of carbon dioxide, which means that the side with less number of moles is the reactants side.
BaCO3 (s) + heat -----> BaO (s) + 1 mole CO2 (g)
Total moles of reactants in gas phase: 0 <=> Total moles of products in gas phase: 1
- Increase volume
Shift equilibrium to the right (to products).
Here we have a different thing, this is contrary to previous one (increase pressure). In a reaction involving gases when the volume increases the pressure decrease favoring the side with the larger number of moles.
As we said before, we only see the compounds present in gas phase.
As we can see the left side has zero moles of gas and the right side has 1 mole of carbon dioxide, which means that the side with larger number of moles is the products side. So the equilibrium will shift to the right favoring products.
- Add CO2 (g)
Shift equilibrium to the left (to reactants).
Since we are adding a gas present in the reaction (in products side), the increase in concentration of that component will shift the reaction to the left to try to counteract the change by reducing that increased concentration, thereby increasing amounts of components on the opposite side of the reaction (reactans).
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