Question

In the equilibrium system below, which of the following changes would cause the equilibrium position to shift to the right?

2SO3(g) Two arrows stacked on top of each other. The top arrow points to the right. The bottom arrow points to the left. 2SO2(g) + O2(g) deltaH = +197 kJ/mol

A) decrease the temperature
B) increase the volume
C) add more O2 gas
D) add a catalyst

Answer 1

B. Increase the volume (in other words, decrease the pressure).
A is wrong because as temperature decreases, the reaction will shift to the left as the system is endothermic (positive delta H).
C. is wrong because as O2 gas is added, the reaction will shift to the left in order to relieve the stress on the system.
D. is wrong because a catalyst will increase the rate of the reaction by decreasing the activation energy. It doesn't affect equilibrium.
B is correct because the left side has two moles of gas while the right side has three moles of gas. Thus, when pressure is decreased (volume is increased--they are inversely related), the system will shift in the direction with more moles of gas.

Answer 2

Answer: The correct answer is Option B.

Explanation: Any change in the equilibrium is studied on the basis of Le-Chatelier's principle.

This principle states that if there is any change in the variables of the reaction, the equilibrium will shift in the direction to minimize the effect.

For the given equation:

`2SO_3+197kJ/mol\leftrightharpoons 2SO_2+O_2`

This is a type of Endothermic reaction because heat is absorbed in the reaction.

For the given options:

Option A: Decrease the temperature

If the temperature is increased, so according to the Le-Chatlier's principle , the equilibrium will shift in the direction where increase in temperature occurs. As, this is an endothermic reaction, forward reaction will decrease the temperature. Hence, the equilibrium will shift in the left direction.

Option B: Increase the volume

If the volume of the container is increased, the pressure will decrease according to Boyle's Law. Now, according to the Le-Chatlier's principle, the equilibrium will shift in the direction where increase in pressure is taking place. As the number of moles of gas molecules is greater at the product side. So, the equilibrium will shift in the right direction.

Option C: Add more
`O_2` gas

If the concentration of
`O_2` that is the product is increased, so according to the Le-Chatlier's principle, the equilibrium will shift in the direction where decrease of concentration of
`O_2` takes place. Therefore, the equilibrium will shift in the left direction.

Option D: Add a catalyst

Role of catalyst is to attain the equilibrium quickly without disturbing the state of equilibrium. Hence, addition of catalyst will not change the equilibrium of the reaction.

From the above explanation, we can easily say that the correct answer is Option B.