Consider the following chemical equilibrium:
SO3(g) --> SO2(g) + 1/2 O2(g) and Delta H = 98.9J
a. Predict weather the forward or reverse reaction will occur when the equilibrium is disturbed by:
i. adding oxygen gas
ii. compressing the system at constant temperature
iii. adding argon gas
iv. removing sulfur dioxide gas
v. decreasing the temperature
b. Which of the above (i-v) will decrease the value of K?
All of this has to do with Le Chatlier's Principle. Tell us what you don't understand about the problem. We can help you through it but there is no point in telling you what you already know.
To determine whether the forward or reverse reaction will occur when the equilibrium is disturbed, we need to consider Le Chatelier's Principle. Le Chatelier's Principle states that when a system at equilibrium is subjected to an external stress, the equilibrium will shift in a way that reduces the impact of that stress.
a. (i) Adding oxygen gas:
In this case, the equilibrium will shift to the left (reverse reaction) to counteract the increased concentration of oxygen. The excess oxygen will react with the SO2 and O2 on the right side of the equation, effectively decreasing the concentration of those products and shifting the equilibrium.
(ii) Compressing the system at constant temperature:
When the system is compressed, the volume decreases. According to Le Chatelier's Principle, the equilibrium will shift in the direction that reduces the number of gas molecules. In this case, the equilibrium will shift to the right (forward reaction) to decrease the total number of gas molecules in the system.
(iii) Adding argon gas:
Argon is an inert gas and does not participate in the reaction. Therefore, adding argon gas will have no effect on the equilibrium position. The concentrations of SO3, SO2, and O2 will remain the same.
(iv) Removing sulfur dioxide gas:
By removing sulfur dioxide (SO2) gas, the equilibrium will shift to the right (forward reaction) to replace the lost SO2. This shift helps maintain the equilibrium by increasing the concentration of SO2 until a new equilibrium is established.
(v) Decreasing the temperature:
Lowering the temperature of the system will favor the exothermic reaction (forward reaction) because it releases heat. The equilibrium will shift to the right, favoring the formation of SO2 and O2.
b. None of the disturbances mentioned (i-v) directly affect the value of K (the equilibrium constant). The equilibrium constant, K, is only affected by temperature. By altering the temperature, the equilibrium constant can be changed. Increasing the temperature usually shifts the equilibrium towards the endothermic reaction, while decreasing the temperature favors the exothermic reaction. Hence, only changing the temperature can directly affect the value of K, while other disturbances indirectly affect the equilibrium position without changing the equilibrium constant itself.