Question: Calculate the heat of reaction $\Delta H$ for the following reaction:
$H_2(g) + Cl_2(g) \to 2 HCl(g)$
You can find a table of bond energies by using the Data button on the ALEKS toolbar.
Round your answer to the nearest kJ/mol.
1. **State the problem:** Calculate the heat of reaction $\Delta H$ for the reaction:
$$H_2(g) + Cl_2(g) \to 2 HCl(g)$$
2. **Formula used:** The heat of reaction can be estimated using bond energies:
$$\Delta H = \sum \text{Bonds broken} - \sum \text{Bonds formed}$$
3. **Identify bonds broken and formed:**
- Bonds broken: 1 $H-H$ bond and 1 $Cl-Cl$ bond
- Bonds formed: 2 $H-Cl$ bonds
4. **Use bond energy values (in kJ/mol):**
- $H-H$ bond energy = 436 kJ/mol
- $Cl-Cl$ bond energy = 243 kJ/mol
- $H-Cl$ bond energy = 431 kJ/mol
5. **Calculate total energy for bonds broken:**
$$436 + 243 = 679 \text{ kJ/mol}$$
6. **Calculate total energy for bonds formed:**
$$2 \times 431 = 862 \text{ kJ/mol}$$
7. **Calculate $\Delta H$:**
$$\Delta H = 679 - 862 = -183 \text{ kJ/mol}$$
8. **Interpretation:** The negative sign indicates the reaction is exothermic.
**Final answer:**
$$\boxed{-183 \text{ kJ/mol}}$$