19. Chemical Thermodynamics
Entropy
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Here it says select a substance with greatest molar entropy. So remember, when comparing the entropies of different substances, the first thing we look at is their phase. So gases have the most entropy, then liquids, then solids. If we take a look at our options here, we have 3 gases. They would have the greatest entropy, so that means a is out, b is out, and d is out. The next thing we look at to break the tie is their complexity. Basically, the more atoms comprising the substance, the greater its entropy. Ammonia has 4 atoms involved because it has 1 nitrogen and 3 hydrogens. Carbon dioxide only has 3 atoms since it's 1 carbon and 2 oxygens, and sulfur trioxide has 4 atoms because it's 1 sulfur and 3 oxygens. So e is out. Now we see that ammonia and sulfur trioxide have the same complexity, so the last thing we look at to break the tie is their mass. The greater the mass of the substance, the greater the entropy. Here, if we compare the mass of ammonia versus sulfur trioxide, sulfur trioxide weighs more. Therefore, it's going to have the higher molar entropy. So here, the answer is option f.
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