Le Chatelier's Principle states that if a change of condition (like temperature) is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. When we're talking about temperature, think of heat as a reactant or product. If you increase the temperature (add heat), the equilibrium will shift to consume the heat. If you decrease the temperature (remove heat), the equilibrium will shift to produce heat. This shift impacts the concentrations of reactants and products at equilibrium.
For example, consider a reaction where heat is a product (exothermic): $A \rightleftharpoons B + \text{Heat}$. Increasing the temperature will shift the equilibrium to the left, favoring the reactants. Conversely, for a reaction where heat is a reactant (endothermic): $A + \text{Heat} \rightleftharpoons B$. Increasing the temperature will shift the equilibrium to the right, favoring the products.
Match the term with its correct definition:
| Term | Definition |
|---|---|
| 1. Equilibrium | 2. A state where the rates of forward and reverse reactions are equal. |
| 2. Endothermic | 5. A reaction that absorbs heat. |
| 3. Exothermic | 3. A reaction that releases heat. |
| 4. Le Chatelier's Principle | 4. States that a system at equilibrium will shift to relieve stress. |
| 5. Shift | 1. A change in the concentrations of reactants and products to re-establish equilibrium. |
Complete the following paragraph using the words: endothermic, exothermic, heat, equilibrium, and shift.
Le Chatelier's Principle helps us predict how a system at _________ will respond to changes in temperature. In an _________ reaction, _________ is absorbed, so increasing the temperature will cause the _________ to favor the products. Conversely, in an _________ reaction, heat is released, so increasing the temperature will favor the reactants.
Answer: Le Chatelier's Principle helps us predict how a system at equilibrium will respond to changes in temperature. In an endothermic reaction, heat is absorbed, so increasing the temperature will cause the shift to favor the products. Conversely, in an exothermic reaction, heat is released, so increasing the temperature will favor the reactants.
Consider the following reversible reaction: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) + \text{92 kJ}$. This reaction is used to produce ammonia. How would increasing the temperature affect the production of ammonia? Explain your reasoning based on Le Chatelier's Principle.
Answer: Increasing the temperature would decrease the production of ammonia. Since the forward reaction is exothermic (releases heat), adding heat will shift the equilibrium to the left, favoring the reactants ($N_2$ and $H_2$) and reducing the yield of ammonia ($NH_3$).
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