Question

Calculate the enthalpy change for the reaction below using Hess's Law: 2CO(g) + O2(g) -> 2CO2(g), delta H = -566 kJ/mol Given the following reactions and their corresponding enthalpy changes: CO(g) + 1/2O2(g) -> CO2(g), delta H = -283 kJ/molC(s) + O2(g) -> CO2(g), delta H = -393.5 kJ/mol

Answer 1

To use Hess's Law, we need to manipulate the given reactions so that they add up to the target reaction: 2CO g  + O2 g  -> 2CO2 g . First, we notice that the target reaction has 2CO2 g  as a product, while the given reactions have only 1CO2 g  as a product. Therefore, we need to multiply the first given reaction by 2:2[CO g  + 1/2O2 g  -> CO2 g ], delta H = 2 -283 kJ/mol  = -566 kJ/molNow, the manipulated reaction is:2CO g  + O2 g  -> 2CO2 g , delta H = -566 kJ/molThis is the same as the target reaction, so the enthalpy change for the target reaction is -566 kJ/mol.