Answer:
Step-by-step explanation:
To calculate the enthalpy change (∆H) for a chemical reaction, you need to know the enthalpies of formation (∆Hf) of the reactants and products involved. The enthalpy change can be determined using Hess's Law, which states that the total enthalpy change for a reaction is the sum of the enthalpies of formation of the products minus the sum of the enthalpies of formation of the reactants.
The balanced chemical equation is:
2 HI → I2 + H2
Now, let's look up the enthalpies of formation for each compound involved in the reaction:
∆Hf (HI) = -169.3 kJ/mol
∆Hf (I2) = 0 kJ/mol (elemental state, so ∆Hf = 0)
∆Hf (H2) = 0 kJ/mol (elemental state, so ∆Hf = 0)
Now, apply Hess's Law to calculate the enthalpy change:
∆H = Σ∆Hf(products) - Σ∆Hf(reactants)
∆H = [∆Hf (I2) + ∆Hf (H2)] - [2 * ∆Hf (HI)]
∆H = [0 + 0] - [2 * (-169.3)]
∆H = 0 + 338.6
∆H ≈ 338.6 kJ/mol
The enthalpy change (∆H) for the reaction 2 HI → I2 + H2 is approximately 338.6 kJ/mol.