Question

Identify the incorrect statement

A) At equilibrium the concentration of the rectants is equal to the concentration of the products

B) A change in temp will change the value of the equilibrium constant

C) Removing reactants from a system at equilibrium shifts the reaction left

D) Decreasing the pressure of a system at equilibrium shifts the reaction tward the side with the most gas molecules

E) All of the above are correct

Please explain how you got your answer

Answer 1

Ans is E

Le Chatelier's Principle is a very useful tool to predict the direction of the equilibrium. There are mainly 3 factors which disturbs the equilibrium.
1) Change in concentration
2) Change in pressure (by changing volume)
3) Change in temperature

I will explain the effects of these changes by using Le Chatelier's Principle.
The application is rather simple. If something increases, try to decrease it. If something decreases, try to increase it.

I will use the following reaction to explain all these effects.

2SO2(g) + O2(g) ↔ 2SO3(g) .......... ΔH = −197 kJ

1) Change in concentration:
- If more O2 is added to the system at equilibrium, the system will try to decrease the added O2. Therefore the equilibrium shifts to right. That is forward reaction will be effective. SO2 and O2 will react and will produce more SO3.
- Same thing occurs when more SO2 is added.
- If more SO3 is added. the system will try to decrease the added SO3. Therefore the equilibrium shifts to left. That is reverse reaction will be effective. SO3 will decompose into SO2 and O2.
- If some SO3 is removed from the system at equilibrium, the system will try to increase the removed SO3. Therefore the equilibrium shifts to right. That is forward reaction will be effective. SO2 and O2 will react to form SO3.
- If some SO2 is removed from the system at equilibrium, the system will try to increase the removed SO2. Therefore the equilibrium shifts to left. That is reverse reaction will be effective. SO3 will decompose into SO2 and O2.

2) Change in pressure (by changing volume)
- If the pressure of the system is increased by decreasing the volume, the system will try to decrease the pressure. Since the partial pressures of gases are directly proportional to their number of moles, the equilibrium shifts to right. Why? Because, at the right there are 2 moles, at the left there are 4 moles. As the number of moles decreases, the pressure also decreases.
- If the pressure of the system is decreased by enlarging the volume, the system will try to increase the pressure. The reverse of the first case will happen.
- Same thing occurs when some O2 is removed.

3) Change in temperature
- If the temperature of the system is increased, the system will try to decrease this increase by consuming heat. Since the forward reaction is exothermic (ΔH = −197 kJ), the reverse reaction will be effective. The equilibrium will shift to left. Endothermic reverse reaction will consume heat.
- If the temperature of the system is decreased, the system will try to increase this decrease by poducing heat. Since the forward reaction is exothermic (ΔH = −197 kJ), the forward reaction will be effective. The equilibrium will shift to right. Exothermic forward reaction will produce heat.
In cases of concentration or pressure changes, the system will readjust itself to satisfy Kc or Kp value.
But, in case of temperature changes, the value of Kc or Kp changes. Whenever equilibrium shifts to right by the effect of temperature change, Kc and Kp will be greater and whenever equilibrium shifts to left by the effect of temperature change, Kc and Kp will be smaller.