What effect (shift to the right or left) does an increase in temperature have on each of the following systems at equilibrium?
a) 3O2(g) ==> 2O3 (g)
<==
Delta H = 284 KJ
b) 2SO3(g) + O2(g) ==> 2SO3(g)
<==
Delta H = -198.2 KJ
When heat is involved, I find it helpful to rewrite the equation with the heat shown; i.e.,
3O2(g) ==> 2O3 (g)
<==
Delta H = 284 KJ
I would rewrite this as
3O2 + heat ==> 2O3. Then adding heat is the same as adding O2. It will shift to the right.
2SO3(g) + O2(g) ==> 2SO3(g)
<==
Delta H = -198.2 KJ
I would rewrite as2SO3 + O2 --< 2SO3 + heat.
Therefore, adding heat will shift the equilibrium to the left.
a) For the reaction 3O2(g) ==> 2O3(g), if the temperature increases, the equilibrium position will shift to the left. This means that more reactants (O2) will be formed and less product (O3) will be formed. The reaction is exothermic (Delta H = 284 KJ), so an increase in temperature will favor the endothermic direction which consumes heat.
b) For the reaction 2SO3(g) + O2(g) ==> 2SO3(g), if the temperature increases, the equilibrium position will shift to the right. This means that more products (SO3) will be formed and less reactants (SO3 and O2) will be formed. The reaction is exothermic (Delta H = -198.2 KJ), so an increase in temperature will favor the exothermic direction which releases heat.
To determine the effect of temperature changes on the position of equilibrium for each system, we need to consider the principle of Le Chatelier. This principle states that if a system at equilibrium is subjected to a change in temperature, pressure, or concentration, the system will adjust to counteract that change.
a) For the reaction: 3O2(g) ==> 2O3(g)
Delta H = +284 KJ (endothermic reaction)
- Increase in Temperature:
When the temperature is increased, the system will try to counteract this change by absorbing the excess heat. In an endothermic reaction like this one, heat is part of the reactants' side. Therefore, increasing the temperature will favor the reactants' side. As a result, the equilibrium will shift to the left, towards the reactants, to consume the excess heat. This means the reaction will produce more O2(g) and less O3(g), resulting in a shift to the left.
- Decrease in Temperature:
Conversely, a decrease in temperature will lead to the system trying to increase the heat to compensate for the change. In an endothermic reaction, heat is absorbed from the surroundings, so reducing the temperature will favor the products' side. The equilibrium will then shift to the right, towards the products, to release more heat. Consequently, the reaction will produce more O3(g) and less O2(g), resulting in a shift to the right.
b) For the reaction: 2SO3(g) + O2(g) ==> 2SO3(g)
Delta H = -198.2 KJ (exothermic reaction)
- Increase in Temperature:
In an exothermic reaction like this one, heat is a product. Increasing the temperature will cause the system to counteract this by absorbing the excess heat. To do so, the equilibrium will shift to the left, favoring the reactants' side to consume some of the excess heat. Consequently, the reaction will produce more SO3(g) and less O2(g), resulting in a shift to the left.
- Decrease in Temperature:
On the other hand, a decrease in temperature will lead the system to try to compensate for the change by releasing more heat. In an exothermic reaction, lowering the temperature will favor the products' side. The equilibrium will then shift to the right, towards the products, to generate more heat. Therefore, the reaction will produce more O2(g) and less SO3(g), resulting in a shift to the right.
In summary, for an endothermic reaction, an increase in temperature shifts the equilibrium to the left, while a decrease in temperature shifts it to the right. For an exothermic reaction, an increase in temperature shifts the equilibrium to the right, and a decrease in temperature shifts it to the left.