Question

Use average bond energies to calculate ΔHrxn for the following hydrogenation reaction: H2C=CH2(g)+H2(g)→H3C−CH3(g) Express your answer in kilojoules per mole to three significant figures. View Available Hint(s)for Part A Hint 1for Part A. How to approach the problem Hint 2for Part A. Simplify: Determine the number and types of bonds broken and formed in the reaction Hint 3for Part A. Interactive worked example: Calculating ΔHrxn from Bond Energies Activate to select the appropriates template from the following choices. Operate up and down arrow for selection and press enter to choose the input value typeActivate to select the appropriates symbol from the following choices. Operate up and down arrow for selection and press enter to choose the input value type ΔHrxn =

Answer 1

The enthalpy change (ΔHrxn) of the hydrogenation reaction is calculated by considering the bond energies of the bonds broken and formed, using the formula ΔHrxn = ∑ Dbroken - ∑ Dformed.

Step-by-step explanation:

The calculation of the enthalpy change, ΔHrxn, for the hydrogenation reaction using average bond energies involves considering the bonds broken and formed. First, we need to identify the bonds broken in the reactants: one C=C bond in ethene (H2C=CH2) and one H-H bond in hydrogen (H2). Then, we calculate the bond energy required to break these bonds. Next, we need to consider the bonds formed in the product, which are four C-H bonds in ethane (H3C-CH3).

Using average bond energies, we can find ΔHrxn using the formula: ΔHrxn = ∑ Dbroken - ∑ Dformed. A negative ΔHrxn value would indicate that the reaction is exothermic, where bond formation releases more energy than is needed to break the initial bonds.

Answer 2

I didn't quite understand but this is my answer:

Step-by-step explanation:

To calculate ΔHrxn for the hydrogenation reaction H2C=CH2(g) + H2(g) → H3C-CH3(g) using average bond energies, we need to determine the number and types of bonds broken and formed in the reaction.

Here's how to approach the problem:

1. Identify the bonds in the reactants and products:

- H2C=CH2 contains a carbon-carbon double bond (C=C) and two carbon-hydrogen bonds (C-H).

- H2 contains a hydrogen-hydrogen bond (H-H).

- H3C-CH3 contains a carbon-carbon single bond (C-C) and six carbon-hydrogen bonds (C-H).

2. Determine the bond energies:

- The average bond energies are typically given in kilojoules per mole (kJ/mol).

- The average bond energies for the C=C bond, C-H bond, and H-H bond are:

- C=C bond: 612 kJ/mol

- C-H bond: 413 kJ/mol

- H-H bond: 436 kJ/mol

3. Calculate the energy change for the bonds broken and formed:

- Bonds broken: We have one C=C bond and one H-H bond.

- Bonds formed: We have one C-C bond and eight C-H bonds (four on each side).

4. Calculate the energy change (ΔHrxn):

- ΔHrxn = (Energy of bonds broken) - (Energy of bonds formed)

Let's calculate ΔHrxn using the average bond energies:

ΔHrxn = (1 × 612 kJ/mol) + (1 × 436 kJ/mol) - (1 × 346 kJ/mol) - (8 × 413 kJ/mol)

Calculating the values:

ΔHrxn = 612 kJ/mol + 436 kJ/mol - 346 kJ/mol - 3304 kJ/mol

= -2602 kJ/mol

Therefore, the ΔHrxn for the hydrogenation reaction is approximately -2602 kJ/mol.