Count the Gas Before You Open the Table

You'll learnhow to compute ΔS° from tabulated absolute entropies, and how to call its sign before doing any arithmetic.

Four moles of gas go into ammonia synthesis and two come out. That one observation settles the sign of ΔS° before a single number is looked up — and it is also the check that catches the two errors this topic is famous for. Twelve short steps; press Next for each one.

12 STEPS · 6 QUICK CHECKS · ΔS° = ΣnS°(prod) − ΣnS°(react) · 298 K, 1 bar · v2

count the gas, then sum each side with its coefficients

Before you start

What you're looking at

A tally of the gas moles on each side of ammonia synthesis, and then a ledger of entropies.

The question

Four moles of gas become two. Can you call the sign of ΔS° before adding anything up?

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