To determine whether the reaction \( \text{CH}_2\text{O}_2 \rightarrow \text{H}_2 + \text{CO}_2 \) is exothermic or endothermic, we need to compare the total bond energies of the reactants with the total bond energies of the products.
Let's first identify the bonds in the reactants (CH₂O₂) and products (H₂ and CO₂):
Reactants: CH₂O₂
- C - H (2 bonds): \( 2 \times 413\ \text{kJ/mol} = 826\ \text{kJ/mol} \)
- C = O (1 bond): \( 745\ \text{kJ/mol} \)
- O - H (2 bonds): \( 2 \times 467\ \text{kJ/mol} = 934\ \text{kJ/mol} \)
Total bond energy for reactants: \[ 826 + 745 + 934 = 2505\ \text{kJ/mol} \]
Products: H₂ and CO₂
- H - H (1 bond): \( 432\ \text{kJ/mol} \)
- C = O (2 bonds) in CO₂: \( 2 \times 745\ \text{kJ/mol} = 1490\ \text{kJ/mol} \)
Total bond energy for products: \[ 432 + 1490 = 1922\ \text{kJ/mol} \]
Energy Calculation:
Now, we can analyze the energy changes:
- Energy absorbed to break bonds (in reactants): 2505 kJ/mol
- Energy released when new bonds are formed (in products): 1922 kJ/mol
Net Energy Change:
To find the overall energy change, we calculate: \[ \text{Net energy change} = \text{Energy absorbed} - \text{Energy released} \] \[ = 2505\ \text{kJ/mol} - 1922\ \text{kJ/mol} = 583\ \text{kJ/mol} \]
Since the energy absorbed is greater than the energy released, this reaction is endothermic.
Thus, the best statement that describes the reaction is:
This reaction is endothermic because more energy is absorbed by the reactants to break bonds than released by the products when new bonds form.
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