Question

Given the reactions (1) and (2) below, determine (i) Delta_r H and Delta_r U for reaction (3), (ii) Delta_f H for both HI(g) and H20(g) all at 298 K. H_2(g)+I_2(s) rightarrow 2HI(g) Delta_r H = +52.96 kJ mol^-1 2 H_2(g) + O_2(g) rightarrow 2 H_2O(g) Delta_r H = -483.64 kJ mol^-1 4 HI(g) + O_2(g) rightarrow 2I_2(s) + 2 H_2O(g)

Answer 1

To determine the standard enthalpy change, ΔrH, and the standard internal energy change, ΔrU, for reaction (3), use Hess's Law. Manipulate reactions (1) and (2) to obtain reaction (3), then calculate the enthalpy changes using the given values. To find the standard enthalpy of formation, ΔfH, for HI(g) and H2O(g) at 298 K, use the enthalpy change equation.

Step-by-step explanation:

To determine the standard enthalpy change, ΔrH, and the standard internal energy change, ΔrU, for reaction (3), we need to use Hess's Law. We can manipulate reactions (1) and (2) to obtain reaction (3).

Multiply reaction (1) by 4 and reverse reaction (2) to obtain:

4HI(g) + O2(g) → 2I2(s) + 2H2O(g)

The standard enthalpy change, ΔrH, for reaction (3) is the sum of the standard enthalpy changes for the individual reactions:

ΔrH = 4ΔrH (reaction (1)) + ΔrH (reaction (2))

To find the standard enthalpy of formation, ΔfH, for HI(g) and H2O(g) at 298 K, we need to use the enthalpy change equation:

ΔrH = ΔfH (products) - ΔfH (reactants)

By substituting the given values for ΔrH into the equation, we can find the enthalpy changes for the reactions.