Question 13
In the reaction:
\[ 2CO + O_2 → 2CO_2 \]
The total bond energy found in all the bonds of carbon dioxide (CO₂) together is 1,472 kJ.
Since CO₂ has two carbon-oxygen double bonds, the bond energy of each carbon-oxygen double bond in carbon dioxide is:
\[
\text{Bond energy of each C=O double bond} = \frac{1,472 , \text{kJ}}{2} = 736 , \text{kJ}
\]
So for the bond energy of each carbon-oxygen double bond in carbon dioxide, you write: 736 kJ.
Question 14
For the reaction:
\[ \text{CH}_4 + 4\text{Cl}_2 → \text{CCl}_4 + 4\text{HCl} \]
To determine whether this reaction is endothermic or exothermic, we first find the total bond energies in both the reactants and products:
Bonds Broken (Reactants):
- 4 (H–C) bonds: \( 4 \times 413 , \text{kJ/mol} = 1,652 , \text{kJ} \)
- 4 (Cl–Cl) bonds: \( 4 \times 243 , \text{kJ/mol} = 972 , \text{kJ} \)
Total energy of the bonds broken (Reactants) = \( 1,652 + 972 = 2,624 , \text{kJ} \)
Bonds Formed (Products):
- 4 (C–Cl) bonds: \( 4 \times 327 , \text{kJ/mol} = 1,308 , \text{kJ} \)
- 4 (H–Cl) bonds: \( 4 \times 427 , \text{kJ/mol} = 1,708 , \text{kJ} \)
Total energy of the bonds formed (Products) = \( 1,308 + 1,708 = 3,016 , \text{kJ} \)
Change in Bond Energy:
- Energy absorbed = energy of the bonds broken - energy of the bonds formed
- \( 2,624 , \text{kJ} - 3,016 , \text{kJ} = -392 , \text{kJ} \)
Since the total bond energy of the reactants (2,624 kJ) is less than that of the products (3,016 kJ), this indicates that energy is released in the reaction.
The correct statement is:
The reaction is exothermic because the total bond energy of the reactants is less than the total bond energy of the products.
1 answer