Enthalpy Formation

Question

A scientist measures the standard enthalpy change for the following reaction to be -783.2 kJ :

2CO(g) + 2 NO(g)2CO₂(g) + N₂(g)

Based on this value and the standard enthalpies of formation for the other substances, the standard enthalpy of formation of CO₂(g) is  kJ/mol.

Answer 1

For this we need to know (look up) the standard enthalpy of formation for CO and NO. The standard enthalpy of formation for N₂ is zero and then we set -783.2 kJ = ∑products - ∑reactants

783.2 kJ = 2ΔH_fCO₂ - (2ΔH_fCO + 2ΔH_fNO)

plug in the tabular values for ΔH_f for CO and for NO and solve for ΔH_f for CO₂