Consider the following equation in chemical equilibrium: [tex]$C_2 H_4(g)+H_2(g) \Leftrightarrow C_2 H_6(g)+137 kJ$[/tex]
What happens to the amount of ethane ([tex]$C_2 H_6$[/tex]) when the temperature of the system is increased?
A. The amount of ethane decreases.
B. The amount of ethane increases initially and then decreases.
C. The amount of ethane increases.
D. The amount of ethane decreases initially and then increases.
Answer (2)
The reaction is exothermic: C 2 H 4 ( g ) + H 2 ( g ) ⇔ C 2 H 6 ( g ) + 137 k J .
Increasing temperature favors the endothermic (reverse) reaction.
The reverse reaction consumes C 2 H 6 .
Therefore, the amount of ethane decreases. The amount of ethane decreases.
Explanation
Understanding the Problem We are given a chemical reaction in equilibrium:
C 2 H 4 ( g ) + H 2 ( g ) ⇔ C 2 H 6 ( g ) + 137 k J
We need to determine what happens to the amount of ethane ( C 2 H 6 ) when the temperature of the system is increased.
Applying Le Chatelier's Principle The reaction is exothermic in the forward direction, meaning it releases heat (137 kJ). According to Le Chatelier's principle, if we increase the temperature of the system, the equilibrium will shift in the direction that absorbs heat to counteract the change.
Determining the Shift in Equilibrium Since the forward reaction is exothermic, the reverse reaction (from ethane to ethene and hydrogen) is endothermic (absorbs heat). Therefore, increasing the temperature will favor the reverse reaction.
Concluding the Effect on Ethane The reverse reaction consumes ethane ( C 2 H 6 ) and produces ethene ( C 2 H 4 ) and hydrogen ( H 2 ). As a result, the amount of ethane will decrease when the temperature is increased.
Final Answer Therefore, the amount of ethane decreases.
Examples
Consider a scenario where you're brewing beer. The fermentation process, like our chemical reaction, is sensitive to temperature. If the fermentation produces too much heat (like the +137 kJ in our reaction), increasing the surrounding temperature will shift the equilibrium, potentially leading to unwanted byproducts and affecting the beer's flavor. By understanding Le Chatelier's principle, brewers can carefully control the temperature to ensure the desired outcome, optimizing the production of the desired compounds and minimizing the undesired ones. This principle applies not only to brewing but also to many industrial chemical processes where precise control of reaction conditions is crucial for maximizing yield and minimizing waste.
Increasing the temperature of the system shifts the equilibrium of the exothermic reaction to favor the reverse reaction, which absorbs heat. This causes a decrease in the amount of ethane ( displaymath{C_2H_6}) in the system. Thus, the correct answer is A. The amount of ethane decreases.
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