Calculate the heat of reaction (ΔHrxn) for the following reaction:
5O2(g) + 4NH3(g) → 6H2O(g) + 4NO(g)
dH rxn = (n*dHo formation products) - (n*dHo reactants)
Post your work if you get stuck.
To calculate the heat of reaction (ΔHrxn) for a chemical reaction, we need to follow a few steps:
Step 1: Determine the heat of formation (∆Hf) values for all the compounds involved in the reaction. The heat of formation is the enthalpy change when one mole of a compound is formed from its elements in their standard states.
Step 2: Identify the stoichiometric coefficients of the reactants and products in the balanced chemical equation.
Step 3: Use the stoichiometric coefficients and ∆Hf values to calculate the ΔHrxn for the reaction using the following formula:
ΔHrxn = Σ(n∆Hf(products)) - Σ(n∆Hf(reactants))
where Σ represents the summation of all terms, n represents the stoichiometric coefficients, and ∆Hf represents the heat of formation.
Let's calculate the ΔHrxn for the given reaction:
1. Determine the heat of formation (∆Hf) values:
∆Hf(O2) = 0 kJ/mol (Oxygen exists as O2 in its standard state)
∆Hf(NH3) = -46.19 kJ/mol
∆Hf(H2O) = -241.82 kJ/mol
∆Hf(NO) = 90.4 kJ/mol
2. Balanced equation:
5O2(g) + 4NH3(g) → 6H2O(g) + 4NO(g)
3. Calculate ΔHrxn:
ΔHrxn = [6∆Hf(H2O) + 4∆Hf(NO)] - [5∆Hf(O2) + 4∆Hf(NH3)]
= [6(-241.82 kJ/mol) + 4(90.4 kJ/mol)] - [5(0 kJ/mol) + 4(-46.19 kJ/mol)]
= [-1450.92 kJ/mol + 361.6 kJ/mol] - [0 kJ/mol + (-184.76 kJ/mol)]
= -1089.32 kJ/mol - (-184.76 kJ/mol)
= -1089.32 kJ/mol + 184.76 kJ/mol
= -904.56 kJ/mol
Therefore, the heat of reaction (∆Hrxn) for the given reaction is -904.56 kJ/mol.