Consider the following cases of standard enthalpy of reaction ( Hr in kJ mol-1) C2H6(g)+ 72O2(g) 2CO2(g)+3H2O(l) H1 =-1550 C(graphite)+O2(g) CO2(g) H2 =-393.5 H2(g)+ 12O2(g) H2O(l) H3 =-286 The magnitude of H f C2H6(g) is kJ mol-1 (Nearest integer).
Answer
95
Solution
Target: 2C + 3H2 C2H6 ⇒ Hf =2 H2 +3 H3 - H1 (Hess's law)
=2(-393.5)+3(-286)+1550
=-95 kJ mol-1 ⇒ magnitude 95
Answer: 95