- The chemical reaction is exothermic, releasing 137 kJ of heat.
- According to Le Chatelier's Principle, adding heat by increasing the system's temperature shifts the equilibrium to the left to consume the excess heat.
- This shift favors the reactants, leading to a decrease in the concentration of the product, ethane (\(C_2H_6\)).
- The correct choice is \(\boxed{\text{a}}\).
Explanation
- Analysis of the Chemical Reaction and Le Chatelier's Principle
The given chemical equation is \[C_2H_4(g) + H_2(g) \rightleftharpoons C_2H_6(g) + 137 \text{ kJ}\]. The term "+ 137 kJ" on the right side of the equation indicates that the reaction releases heat, identifying it as an exothermic process. Le Chatelier's Principle states that if a system at dynamic equilibrium is disturbed by a change in conditions, the system will adjust its equilibrium position to counteract that disturbance. In this case, increasing the temperature means adding thermal energy to the system.
- Applying Le Chatelier's Principle to Temperature Change
Because the reaction is exothermic, we can treat heat as a product. According to Le Chatelier's Principle, adding heat (by increasing the temperature) disturbs the equilibrium. The system will shift to consume the excess heat. To counteract the addition of heat, the equilibrium will shift to the left, favoring the reverse reaction. As the reaction proceeds in the reverse direction, the products are converted back into reactants. Therefore, the amount of the product, ethane (\(C_2H_6\)), will decrease as it is consumed to absorb the added heat.
- Conclusion
Based on our analysis, increasing the temperature causes the equilibrium to shift to the left, resulting in a decrease in the concentration of the product, ethane (\(C_2H_6\)). Comparing this conclusion to the given options, option (a) states that the amount of ethane decreases, which aligns with our result. Therefore, the correct choice is (a).
Examples
In industrial chemical processes, such as the synthesis of ammonia or the production of ethylene derivatives, controlling temperature is critical. If a desired product is formed through an exothermic reaction, engineers must carefully manage cooling systems. If the temperature is allowed to rise too high, the equilibrium will shift away from the product, reducing the yield of the substance being manufactured, which can lead to inefficient production cycles.