Question

Determine the standard enthalpy of formation of methane (CH4) using Hess's Law, given the following reactions and enthalpy changes: 1. C(graphite) + 2H2(g) -> CH4(g)      ΔH1 = -74.6 kJ/mol 2. 2H2(g) + O2(g) -> 2H2O(l)          ΔH2 = -571.7 kJ/mol 3. C(graphite) + O2(g) -> CO2(g)     ΔH3 = -393.5 kJ/mol.

Answer 1

To determine the standard enthalpy of formation of methane  CH4  using Hess's Law, we need to manipulate the given reactions to form the desired reaction: C graphite  + 2H2 g  -> CH4 g The desired reaction is already given as reaction 1, so we don't need to manipulate any of the reactions. Therefore, the standard enthalpy of formation of methane  CH4  is:Hf CH4  = H1 = -74.6 kJ/mol