Consider the reaction below.
[tex]$C_2 H_4(g)+H_2(g) \rightarrow C_2 H_6(g)$[/tex]
Which change would likely cause the greatest increase in the rate of the reaction?
A. decrease temperature and decrease pressure
B. increase temperature and decrease pressure
C. decrease temperature and increase pressure
D. increase temperature and increase pressure
Answer (1)
Increasing temperature increases the reaction rate by providing more energy to overcome the activation energy.
Increasing pressure favors the side with fewer moles of gas, increasing the reaction rate in this case.
Increasing both temperature and pressure will increase the reaction rate, with temperature having a more significant effect.
Therefore, the greatest increase in the reaction rate will occur when both temperature and pressure are increased. increase temperature and increase pressure
Explanation
Understanding the Reaction The reaction is: C 2 H 4 ( g ) + H 2 ( g ) r i g h t a rro w C 2 H 6 ( g ) . We want to determine which change in temperature and pressure will increase the rate of the reaction the most.
Effect of Temperature Increasing the temperature increases the reaction rate because it provides more energy for the reactant molecules to overcome the activation energy barrier. Decreasing the temperature decreases the reaction rate.
Effect of Pressure In this reaction, 2 moles of gas on the left side react to form 1 mole of gas on the right side. According to Le Chatelier's principle, increasing the pressure will favor the side with fewer moles of gas, which is the product side. Therefore, increasing the pressure will increase the reaction rate. Decreasing the pressure will decrease the reaction rate.
Evaluating the Options Now we evaluate each option:
Decrease temperature and decrease pressure: This will decrease the reaction rate.
Increase temperature and decrease pressure: The temperature increase will increase the rate, but the pressure decrease will decrease the rate. The overall effect is uncertain.
Decrease temperature and increase pressure: The temperature decrease will decrease the rate, but the pressure increase will increase the rate. The overall effect is uncertain.
Increase temperature and increase pressure: This will increase the reaction rate.
Comparing the Effects Increasing the temperature has an exponential effect on the reaction rate (Arrhenius equation), while increasing the pressure has a more linear effect (Le Chatelier's principle). Therefore, increasing the temperature and increasing the pressure will likely cause the greatest increase in the rate of the reaction.
Examples
In industrial chemical production, understanding how temperature and pressure affect reaction rates is crucial for optimizing yield and efficiency. For example, in the Haber-Bosch process for ammonia synthesis ( N 2 + 3 H 2 r i g h t a rro w 2 N H 3 ), high temperature and pressure are used to achieve a reasonable reaction rate and equilibrium yield. By carefully controlling these conditions, manufacturers can maximize the production of desired products while minimizing energy consumption and waste.
