How does the entropy change with the following reaction?

• A. Entropy decreases.
• B. Entropy increases.
• C. Entropy stays the same.
• D. Impossible to tell. Needs more information.

Answer: (A)

Verified step by step guidance

1. Identify the reaction: The given reaction is the synthesis of ammonia from nitrogen and hydrogen gases: N2(g) + 3 H2(g) → 2 NH3(g).
2. Count the number of moles of gas on each side of the reaction: On the reactant side, there are 1 mole of N2 and 3 moles of H2, totaling 4 moles of gas. On the product side, there are 2 moles of NH3.
3. Compare the number of moles of gas: The reaction goes from 4 moles of gas (reactants) to 2 moles of gas (products).
4. Understand the concept of entropy: Entropy is a measure of disorder or randomness. In general, a decrease in the number of gas molecules indicates a decrease in entropy because gases have higher entropy than liquids or solids due to their greater freedom of movement.
5. Conclude the change in entropy: Since the number of gas molecules decreases from 4 to 2, the entropy of the system decreases during this reaction.