Question

What is ΔH∘rxn for the following chemical reaction?

CO(g)+NH3(g)→HCN(g)+H2O(g)

You can use the following table of standard heats of formation (ΔH∘f) to calculate the enthalpy of the given reaction.

Element/ Compound Standard Heat of Formation (kJ/mol) Element/ Compound Standard Heat of Formation (kJ/mol)
H(g) 218 N(g) 473
H2(g) 0 O2(g) 0
NH3(g) −45.90 O(g) 249
CO(g) −110.5 H2O(g) −241.8kJ
C(g) 71 HCN(g) 130.5kJ
C(s) 0 HNO3(aq) −206.6
Express the standard enthalpy of reaction to three significant figures and include the appropriate units.

Answer 1

To calculate the standard enthalpy of reaction (ΔH∘rxn) for the given chemical reaction, we need to use the equation for enthalpy of reaction, which is:

ΔH∘rxn = Σ(ΔH∘f products) - Σ(ΔH∘f reactants)

where ΔH∘f is the standard heat of formation for a given compound, and the summation symbol (Σ) indicates that we need to sum the values for all of the products and reactants in the reaction.

In this case, we are given the standard heats of formation for the products and reactants in the reaction:

CO(g)+NH3(g)→HCN(g)+H2O(g)

We can use these values to calculate the enthalpy of reaction, as follows:

ΔH∘rxn = Σ(ΔH∘f products) - Σ(ΔH∘f reactants)

= (ΔH∘f HCN + ΔH∘f H2O) - (ΔH∘f CO + ΔH∘f NH3)

= (130.5 kJ + −241.8 kJ) - (−110.5 kJ + −45.90 kJ)

= (−111.3 kJ) - (−156.4 kJ)

= 45.1 kJ

Therefore, the standard enthalpy of reaction for the given chemical reaction is 45.1 kJ to three significant figures. This value represents the amount of heat that is absorbed or released when the reactants are converted into products, and it can be used to predict the energetics of the reaction under standard conditions.