Identify from following reactions that it takes place with Δ H = Δ U .

Question

Quantrex Academy · Accepted Answer

Correct answer: A. CO_2(g) + H_2(g) arrow CO(g) + H_2O(g)

The relationship between enthalpy change (\Delta H

) and internal energy change (\Delta U

) is given by:

\Delta H = \Delta U + \Delta n_g RT

For

\Delta H = \Delta U

, the change in the number of moles of gaseous species (\Delta n_g

) must be zero.<br><br>\Delta n_g = \text{moles of gaseous products} - \text{moles of gaseous reactants}

Evaluating

\Delta n_g

for the given reactions:

For

\text{CO}_2(g) + \text{H}_2(g) \rightarrow \text{CO}(g) + \text{H}_2\text{O}(g)

:

\Delta n_g = (1 + 1) - (1 + 1) = 0

For

\text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g)

:

\Delta n_g = 2 - (1 + 3) = -2

For

\text{CO}(g) + \dfrac{1}{2}\text{O}_2(g) \rightarrow \text{CO}_2(g)

:

\Delta n_g = 1 - \left(1 + \dfrac{1}{2}\right) = -0.5

For

\text{H}_2(g) + \dfrac{1}{2}\text{O}_2(g) \rightarrow \text{H}_2\text{O}(l)

:

\Delta n_g = 0 - \left(1 + \dfrac{1}{2}\right) = -1.5

Since

\Delta n_g = 0

only for the first reaction,

\Delta H = \Delta U

for this reaction.

Answer:

\text{CO}_2(g) + \text{H}_2(g) \rightarrow \text{CO}(g) + \text{H}_2\text{O}(g)

Identify from following reactions that it takes place with Δ H = Δ...