Question

Use the reaction and bond information to answer the question.

H2 + CO2 → CH2O2

Reactant bond energies: H–H is 432 kJ/mol, C=O is 799 kJ/mol

Product bond energies: C–H is 413 kJ/mol, C=O is 745 kJ/mol, C–O is 358 kJ/mol, O–H is 467 kJ/mol

How much energy must this system absorb before the reaction can begin?


2,030 kJ

2,462 kJ

1,231 kJ

1,663 kJ

Answer 1

The system must absorb 2030 kJ/mol of energy to break the bonds in the reactants H2 and CO2 before the reaction to form CH2O2 can begin.

Step-by-step explanation:

To determine the amount of energy that must be absorbed by the system before the reaction between H2 and CO2 can begin, we need to calculate the total energy of the bonds that must be broken and compare this with the energy that will be released when new bonds form in the product CH2O2.

• Bond energies of reactants: H–H bond (432 kJ/mol) + C=O double bond in CO2 (2 x 799 kJ/mol)
• Total energy to break bonds in reactants = 432 kJ/mol + (2 x 799 kJ/mol) = 2030 kJ/mol
• Bond energies in the product: 2 x C–H (2 x 413 kJ/mol) + C=O (745 kJ/mol) + C–O (358 kJ/mol) + O–H (467 kJ/mol)
• Total energy released when new bonds form = (2 x 413 kJ/mol) + 745 kJ/mol + 358 kJ/mol + 467 kJ/mol
• However, since the question specifically asks about the initial energy absorption, the relevant figure is the total energy to break bonds in the reactants, which is 2030 kJ/mol.

Answer 2

1 Absorbed

2 O=O

3 2,030 kJ

4 Yes, it would occur without additional energy because the reaction is exothermic.

5 The reaction is endothermic, because stronger bonds are broken than formed.