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Enthalpy and entropy

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Question 3

The table below shows standard entropies, S⊖S^\ominusS⊖, for three gases.

SubstanceS⊖S^\ominusS⊖ / J mol−1K−1\text{J mol}^{-1}\text{K}^{-1}J mol−1K−1
NH3(g)\text{NH}_3(\text{g})NH3​(g)192.8
N2(g)\text{N}_2(\text{g})N2​(g)191.6
H2(g)\text{H}_2(\text{g})H2​(g)130.7

What is the entropy change, ΔS⊖\Delta S^\ominusΔS⊖, in J mol−1K−1\text{J mol}^{-1}\text{K}^{-1}J mol−1K−1, for the catalytic decomposition of ammonia shown below?

2NH3(g)→N2(g)+3H2(g) 2\text{NH}_3(\text{g}) \rightarrow \text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) 2NH3​(g)→N2​(g)+3H2​(g)
A

−198.1-198.1−198.1

B

+129.5+129.5+129.5

C

+198.1+198.1+198.1

D

+390.9+390.9+390.9

Markscheme

Enthalpy and entropy Questions

  1. A Level
  2. /Chemistry
  3. /Enthalpy and entropy

24 exam-style questions on OCR A A Level Chemistry Enthalpy and entropy. Each one has a worked solution and a mark scheme showing where the marks go.

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