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Hydrogen [tex]\(\left( H_2 \right)\)[/tex] reacts with bromine [tex]\(\left( Br_2 \right)\)[/tex] to produce hydrogen bromide [tex]\(( HBr )\)[/tex] gas as shown in the equation below.
[tex]\[ H_2(g) + Br_2(g) \rightarrow 2 HBr (g) \][/tex]

Standard Enthalpies of Formation

\begin{tabular}{|c|c|}
\hline
Substance & [tex]\(\Delta H_f \text{ (kJ/mol)}\)[/tex] \\
\hline
[tex]\(Br_2(l)\)[/tex] & 0.0 \\
\hline
[tex]\(Br_2(g)\)[/tex] & 30.907 \\
\hline
[tex]\(HBr(g)\)[/tex] & -36.4 \\
\hline
[tex]\(HCl(g)\)[/tex] & -92.307 \\
\hline
[tex]\(HI(g)\)[/tex] & 26.48 \\
\hline
[tex]\(H_2(g)\)[/tex] & 0.0 \\
\hline
[tex]\(I_2(g)\)[/tex] & 62.438 \\
\hline
\end{tabular}

Based on the equation and the information in the table, what is the enthalpy of the reaction?


Sagot :

To determine the enthalpy change of the reaction [tex]\( H_2 (g) + Br_2 (g) \rightarrow 2 HBr (g) \)[/tex], we use the concept of standard enthalpies of formation. Here are the steps:

1. Identify the substances and their standard enthalpies of formation involved in the reaction:

From the table:
- [tex]\( \Delta H_f^\circ \)[/tex] for [tex]\( H_2 (g) = 0.0 \, \text{kJ/mol} \)[/tex]
- [tex]\( \Delta H_f^\circ \)[/tex] for [tex]\( Br_2 (g) = 30.907 \, \text{kJ/mol} \)[/tex]
- [tex]\( \Delta H_f^\circ \)[/tex] for [tex]\( HBr (g) = -36.4 \, \text{kJ/mol} \)[/tex]

2. Calculate the total enthalpy of the reactants:

The reactants are [tex]\( H_2 (g) \)[/tex] and [tex]\( Br_2 (g) \)[/tex].
- For [tex]\( H_2 (g) \)[/tex], the enthalpy is [tex]\( 0.0 \, \text{kJ/mol} \)[/tex].
- For [tex]\( Br_2 (g) \)[/tex], the enthalpy is [tex]\( 30.907 \, \text{kJ/mol} \)[/tex].

Total enthalpy of reactants:
[tex]\[ \Delta H_{\text{reactants}} = 0.0 + 30.907 = 30.907 \, \text{kJ} \][/tex]

3. Calculate the total enthalpy of the products:

The product is [tex]\( 2 \, \text{mol} \)[/tex] of [tex]\( HBr (g) \)[/tex].
- For [tex]\( HBr (g) \)[/tex], the enthalpy is [tex]\( -36.4 \, \text{kJ/mol} \)[/tex].

Total enthalpy of products:
[tex]\[ \Delta H_{\text{products}} = 2 \times (-36.4) = -72.8 \, \text{kJ} \][/tex]

4. Determine the enthalpy change of the reaction (ΔH):

[tex]\[ \Delta H_{\text{reaction}} = \Delta H_{\text{products}} - \Delta H_{\text{reactants}} \][/tex]

Plugging in the values:
[tex]\[ \Delta H_{\text{reaction}} = -72.8 - 30.907 = -103.707 \, \text{kJ} \][/tex]

Summary:
- The total enthalpy of reactants is [tex]\( 30.907 \, \text{kJ} \)[/tex].
- The total enthalpy of products is [tex]\( -72.8 \, \text{kJ} \)[/tex].
- The enthalpy change of the reaction is [tex]\( \Delta H = -103.707 \, \text{kJ} \)[/tex].

Therefore, the enthalpy of the reaction is [tex]\( -103.707 \, \text{kJ} \)[/tex].
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