A chemistry student needs to calculate the standard enthalpy change for the combustion reaction of methane (CH4) to produce carbon dioxide (CO2) and water (H2O) at 298 K. The student is given the following information: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ΔH°rxn = -890.4 kJ/molThe enthalpy of formation of CH4(g) and H2O(l) are -74.8 kJ/mol and -285.8 kJ/mol, respectively. Using this data, what is the standard enthalpy change for the combustion reaction of methane (CH4) to produce carbon dioxide (CO2) and water (H2O) at 298 K?

Question

A chemistry student needs to calculate the standard enthalpy change for the combustion reaction of methane (CH4) to produce ca

Answer 1

To calculate the standard enthalpy change for the combustion reaction of methane, we can use the following equation:Hrxn =  Hf products  -  Hf reactants where Hrxn is the standard enthalpy change for the reaction, Hf products  is the sum of the standard enthalpies of formation of the products, and Hf reactants  is the sum of the standard enthalpies of formation of the reactants.First, we need to find the standard enthalpy of formation for CO2 g . We can use the given Hrxn and the enthalpies of formation for CH4 g  and H2O l  to do this:-890.4 kJ/mol = [Hf CO2  + 2  Hf H2O ] - [Hf CH4  + 2  Hf O2 ]Since the standard enthalpy of formation for an element in its standard state  O2 g  in this case  is zero, we can simplify the equation:-890.4 kJ/mol = [Hf CO2  + 2   -285.8 kJ/mol ] -  -74.8 kJ/mol Now, we can solve for Hf CO2 :Hf CO2  = -890.4 kJ/mol + 74.8 kJ/mol - 2   -285.8 kJ/mol Hf CO2  = -393.5 kJ/molNow that we have the standard enthalpy of formation for CO2 g , we can calculate the standard enthalpy change for the combustion reaction of methane:Hrxn = [Hf CO2  + 2  Hf H2O ] - [Hf CH4  + 2  Hf O2 ]Hrxn = [ -393.5 kJ/mol  + 2   -285.8 kJ/mol ] - [ -74.8 kJ/mol  + 2   0 kJ/mol ]Hrxn = -965.1 kJ/molTherefore, the standard enthalpy change for the combustion reaction of methane  CH4  to produce carbon dioxide  CO2  and water  H2O  at 298 K is -965.1 kJ/mol.