To determine whether the reaction is exothermic or endothermic, we need to consider the energy of the bonds broken in the reactants and the energy of the bonds formed in the products.
The given reaction is: \[ \text{CH}_4 + 4\text{Cl}_2 \rightarrow \text{CCl}_4 + 4\text{HCl} \]
Now, let's break it down:
-
Calculation of Bond Energy of Reactants:
- In the reactants:
- Methane (CH4) has 4 C–H bonds.
- Chlorine (Cl2) has 4 Cl–Cl bonds.
- The total bond energy for reactants: \[ \text{Total bond energy (reactants)} = (4 \times 411 , \text{kJ/mol}) + (4 \times 242 , \text{kJ/mol}) \] \[ = 1644 , \text{kJ/mol} + 968 , \text{kJ/mol} = 2612 , \text{kJ/mol} \]
- In the reactants:
-
Calculation of Bond Energy of Products:
- In the products:
- Carbon tetrachloride (CCl4) has 4 C–Cl bonds.
- Hydrogen chloride (HCl) has 4 H–Cl bonds.
- The total bond energy for products: \[ \text{Total bond energy (products)} = (4 \times 327 , \text{kJ/mol}) + (4 \times 427 , \text{kJ/mol}) \] \[ = 1308 , \text{kJ/mol} + 1708 , \text{kJ/mol} = 3016 , \text{kJ/mol} \]
- In the products:
-
Comparison of Total Bond Energies:
- Total bond energy of reactants = 2612 kJ/mol
- Total bond energy of products = 3016 kJ/mol
Since the energy of the bonds in the products is greater than the energy of the bonds in the reactants, the reaction requires energy (it absorbs energy) and is therefore endothermic.
The correct answer is: The reaction is endothermic because the total bond energy of the reactants is less than the total bond energy of the products.
1 answer