# HELP hessβ law questions

Given the following data: (CH4) = -74.8 kJmol', (CH CI) = -134.5 kJmol', (HCI) = -92.3 kJmol-1;
Calculate delta H for the reaction CH4(g) + Cl2(g) -> CH3CI(g) + HCI(g)

Given the data:
4NH3(g) + 302(g) -> 2N2(g) + 6H2O(1), deltaH = -1530kJmol-I
H2(g) + 1/2O2(g) -> H2O(1), deltaH = -288 kJmol-l
Calculate the enthalpy of formation of ammonia.
The enthalpy change for the reaction CH4(g) + Cl2(g) -> CH3CI(g) + HCI(g) can be calculated by using the equation deltaH = deltaHf(products) - deltaHf(reactants).

The enthalpies of formation for the products are:
deltaHf(CH3CI) = -134.5 kJ/mol
deltaHf(HCI) = -92.3 kJ/mol

The enthalpies of formation for the reactants are:
deltaHf(CH4) = -74.8 kJ/mol
deltaHf(Cl2) = 0 kJ/mol (since Cl2 is a diatomic molecule in its standard state)

Therefore, deltaH = (-134.5 + -92.3) - (-74.8 + 0) = -226.8 kJ/mol.

For the second question,
We know deltaH for the reaction 4NH3(g) + 302(g) -> 2N2(g) + 6H2O(1) = -1530 kJmol-1
and deltaH for the reaction H2(g) + 1/2O2(g) -> H2O(1) = -288 kJmol-1

Given the following equations,
4NH3(g) + 5O2(g) -> 4NO(g) + 6H2O(l), deltaH = -902kJmol-1
2NO(g) + O2(g) -> 2NO2(g), deltaH = -57.2 kJmol-1

The enthalpy of formation for ammonia can be calculated as follows:
4NH3(g) + 5O2(g) -> 4NO(g) + 6H2O(1), deltaH = -902 kJmol-1
2NO(g) + O2(g) -> 2NO2(g), deltaH = -57.2 kJmol-1
4NH3(g) + 302(g) -> 2N2(g) + 6H2O(1), deltaH = -1530 kJmol-1
H2(g) + 1/2O2(g) -> H2O(l), deltaH = -288 kJmol-1

Therefore, deltaHf(NH3) = [2N2(g) + 3H2(g) -> 4NH3(g)], deltaHf(NH3) = deltaH(4NH3(g) + 5O2(g) -> 4NO(g) + 6H2O(1)) + deltaH(2NO(g) + O2(g) -> 2NO2(g)) + deltaH(H2(g) + 1/2O2(g) -> H2O(l)) - deltaH(4NH3(g) + 302(g) -> 2N2(g) + 6H2O(1))

deltaHf(NH3) = -902 kJmol-1 + -57.2 kJmol-1 + -288 kJmol-1 - (-1530 kJmol-1) = -2069 kJ/mol
not your question but it has the method used to solve these questions.

since everything is in the gas state and there are no changes of state you can use this method.

https://www.science-revision.co.uk/A-level_enthalpy_changes_bond_enthalpies.html