How much heat is absorbed when 30.00 g of C (s) reacts in the presence of excess SO2 (g) to produce CS2 (l) and CO (g) according to the following chemical equation?

5 C (s) + 2 SO2 (g) → CS2 (l) + 4 CO (g) ΔH° = + 239.9 kJ

120.0 kJ

Explanation:

First we convert the given mass of C to moles:

30.00 g C : 12g/mol = 2.5 mol

The ΔH° value given by the problem, is the heat absorbed when 5 moles of C react.

So when we have half the moles of C (2.5 instead of 5.0), the heat absorbed will also be half, thus the answer is:

239.9 kJ / 2 = 120.0 kJ