Predict whether the equilibria
I) CO(g) + H2O(g) ⇀↽ CO2(g) + H2(g),
∆H
◦ = −41 kJ
II) X2(g) ⇀↽ 2 X(g), where X is a halogen
will shift toward products or reactants with a
temperature increase.
To predict whether the equilibria will shift toward products or reactants with a temperature increase, we can use Le Chatelier's principle.
For reaction I) CO(g) + H2O(g) ⇀↽ CO2(g) + H2(g), the ∆H value is -41 kJ. This indicates that the reaction is exothermic because it releases heat.
According to Le Chatelier's principle, an increase in temperature will favor the endothermic direction of a reaction (where heat is absorbed) to counteract the temperature increase.
Since reaction I) is exothermic, an increase in temperature will shift the equilibrium to favor the reactant side (CO(g) + H2O(g)). Therefore, the equilibrium will shift towards the reactants.
For reaction II) X2(g) ⇀↽ 2 X(g), where X is a halogen, no specific enthalpy change is given. However, halogen reactions are typically considered to be exothermic.
Similarly to reaction I), an increase in temperature will favor the endothermic direction of the reaction. In this case, the endothermic direction corresponds to the formation of X2(g) from X(g).
Therefore, with a temperature increase, the equilibrium of reaction II) will shift towards the reactants (X(g)) to absorb the excess heat.
To predict how the equilibria will shift with a temperature increase, we need to apply Le Chatelier's principle. According to this principle, when a system at equilibrium is subjected to a stress (such as a change in temperature), it will respond in a way that minimizes the effect of the stress.
For the reaction:
I) CO(g) + H2O(g) ⇀↽ CO2(g) + H2(g)
Given that ∆H° = -41 kJ, we know that the reaction is exothermic. An exothermic reaction releases heat, so increasing the temperature would be considered a stress to the system. Since the system wants to minimize this stress, it will shift in the direction that consumes heat. In this case, the forward reaction (towards products) is the direction that consumes heat. Therefore, with a temperature increase, the equilibrium will shift towards the products (CO2 and H2).
For the reaction:
II) X2(g) ⇀↽ 2 X(g), where X is a halogen
In this reaction, we don't have the specific value for ∆H°, but we can make a general assumption. The reaction represents the dissociation of a diatomic halogen gas (X2) into individual halogen atoms (X). Breaking the bond in a diatomic molecule is endothermic because it requires an input of energy. Therefore, this reaction is generally endothermic.
Applying Le Chatelier's principle, if we increase the temperature (which is an input of energy), the system will respond by favoring the reaction that consumes the heat. In this case, the forward reaction (breaking the diatomic molecule) is the one that requires heat. Therefore, with a temperature increase, the equilibrium will shift towards the reactants (X2).
In summary:
- For reaction I, a temperature increase will shift the equilibrium towards the products (CO2 and H2).
- For reaction II, a temperature increase will shift the equilibrium towards the reactants (X2).