Question

Calculate the enthalpy change for the oxidation of methane (CH4) to carbon dioxide (CO2) at constant pressure using the following reactions: * C(s) + O2(g) --> CO2(g)    ΔH = -393.5 kJ/mol* 2H2(g) + O2(g) -->  2H2O(l)   ΔH = -571.6 kJ/molThe enthalpy of formation of CH4(g) is -74.8 kJ/mol.

Answer 1

To calculate the enthalpy change for the oxidation of methane  CH4  to carbon dioxide  CO2 , we need to use Hess's Law. Hess's Law states that the enthalpy change for a reaction is the same whether it occurs in one step or several steps. First, we need to write the balanced equation for the oxidation of methane:CH4 g  + 2O2 g  --> CO2 g  + 2H2O l Now, we need to manipulate the given reactions to match the balanced equation above:1. C s  + O2 g  --> CO2 g     H = -393.5 kJ/mol2. CH4 g  --> C s  + 2H2 g     H = 74.8 kJ/mol  reverse the enthalpy of formation of CH4 3. 2H2 g  + O2 g  -->  2H2O l    H = -571.6 kJ/molNow, we can add reactions 1, 2, and 3 together:C s  + O2 g  + CH4 g  --> CO2 g  + C s  + 2H2 g  + 2H2 g  + O2 g  -->  2H2O l Cancel out the common terms on both sides:CH4 g  + 2O2 g  --> CO2 g  + 2H2O l Now, add the enthalpy changes for the three reactions:H_total = -393.5 kJ/mol + 74.8 kJ/mol - 571.6 kJ/mol = -890.3 kJ/molSo, the enthalpy change for the oxidation of methane  CH4  to carbon dioxide  CO2  at constant pressure is -890.3 kJ/mol.