A chemical plant produces sulfur trioxide in two consecutive reactions at constant pressure, as shown below.
Step 1 S(s) + O₂(g) → SO₂(g) ΔH1=−297kJ
Step 2 2 SO₂(g) + O₂(g) → 2 SO₃(g) ΔH2=−198kJ
Which of the following best explains why the total enthalpy change for converting S(s) to SO₃(g) equals the sum of ΔH1 and ΔH2?
a) Energy is conserved, so the heat released in each step adds to give the overall heat released.
b) Because both steps are exothermic, their negative ΔH values reinforce each other and therefore must be added.
c) Enthalpy is a state function, so the overall ΔH depends only on the initial and final states and is independent of the pathway taken.
d) The intermediate SO2 is formed and consumed, causing its enthalpy to cancel, leaving only the second step to contribute to the overall ΔH.