Given the following at 25°C, calculate for HCN(g) (in kJ/mol) at 25°C.
; ΔH= –870.8 kJ
ΔH = –80.3 kJ/mol for NH₃(g), - 74.6 kJ/mol for CH₄, and - 241.8 kJ/mol for H₂O(g).

The enthalpy of formation of HCN(g) is 135.1 kJ/mol

Explanation:

Enthalpy change is defined as the difference in enthalpies of all the product and the reactants each multiplied with their respective number of moles.

The equation used to calculate enthalpy change is of a reaction is:

For the given chemical reaction:

The equation for the enthalpy change of the above reaction is:

We are given:

Putting values in above equation, we get:

Hence, the enthalpy of formation of HCN(g) is 135.1 kJ/mol

the potential energy of the reactants is 200j.

from the energy diagram, the energy of the product formed is 350j; this means that, this reaction is an endothermic reaction, because it absorbs energy from its environment.