Question

Consider the reaction: \[ \text{N}_2 (g) + 3 \text{H}_2 (g) \rightarrow 2 \text{NH}_3 (g) \] carried out at constant temperature and pressure. If \( \Delta H \) and \( \Delta U \) are the enthalpy and internal energy changes for the reaction, which of the following expressions is true?

• A. \( \Delta H = \Delta U \)
• B. \( \Delta H>\Delta U \)
• C. \( \Delta H<\Delta U \)
• D. \( \Delta H = 0 \)

Hint:

At constant pressure, the enthalpy change \( \Delta H \) is greater than the internal energy change \( \Delta U \) because of the work done against pressure.

Answer 1

The Correct Option is B

Step 1: Use the relation between \( \Delta H \) and \( \Delta U \).
At constant temperature and pressure, \( \Delta H = \Delta U + P\Delta V \). Since the reaction involves a decrease in volume, \( \Delta H \) is greater than \( \Delta U \).
Step 2: Conclusion.
Thus, \( \Delta H>\Delta U \).
Final Answer: \[ \boxed{\Delta H>\Delta U} \]