Question

2. What is the standard enthalpy of formation (∆_f H◦ ) for ethane (C2H6) at 25 ◦C? The following standard rection enthalpies at 25 ◦C are known:

(1) C(s, graphite) + O2(g) → CO2(g), ∆_r H ◦ = −393.5 kJ mol−1

(2) H2(g) + 1 2 O2(g) → H2O(l), ∆r H ◦ = −285.9 kJ mol−1

(3) C2H6(g) + 31 2 O2(g) → 2CO2(g) + 3H2O(l), ∆_r H ◦ = −1560.1 kJ mol−1

The formation reaction of ethane corresponds to the reaction of graphite with hydrogen H2 producing one mole of ethane.