If a system in dynamic equilibrium contains a large excess of reactant, what can be done to encourage the formation of more product?

Question

A.
seal the system so the total quantity of products and reactants stays the same

B.
decrease the supply of reactant to the system

C.
decrease the temperature of the system so it is close to absolute zero

D.
remove product from the system as it is formed

Answer 1

When a system in dynamic equilibrium experiences a stress (change in conditions), the system will react in a way to counteract that stress. This is Le Chatelier's principle.

We want to manipulate the system to react in a way that yields more product. The answer choice that would give this result is choice D. If you remove some of the product, the stress you place on the system is a decrease in product. The system's reaction then is to counteract that stress, by shifting the equilibrium to the right to increase product formation.

 

Why the other choices are wrong:
A. the system is already at equilibrium so sealing it won't change anything
B. if you decrease the supply of reactants, the system will shift to increase the formation of reactants via the reverse reaction which would decrease product
C. to predict the effect of a change in temperature on the system you need to know whether the reaction is endothermic or exothermic, which we don't know. For example, if the forward reaction is exothermic, decreasing the temperature of the system will increase the forward reaction (forming products) in order to generate heat to counteract the decrease in temperature. But we can't say this because we don't know the heat of reaction for this system.