Bond Enthalpies

1.        In the presence of bright light, hydrogen and bromine react. One step in the reaction is shown

            below.

            H₂(g) + Br(g) → HBr(g) + H(g)

            The enthalpy change for this step can be represented as

            A         (H-H bond enthalpy) + (Br-Br bond enthalpy)

            B          (H-H bond enthalpy) − (Br-Br bond enthalpy)

            C          (H-H bond enthalpy) + (H-Br bond enthalpy)

            D         (H-H bond enthalpy) − (H-Br bond enthalpy).

2.        Use the information in the table to calculate the enthalpy change for the following reaction:

H_2(g) + Cl_2(g) à 2HCl_(g)

Bonds	ΔH to break bond (kJ mol-1)
H-H	432
Cl-Cl	243
H-Cl	428

 

3.        Using the bond enthalpy values from your data booklet, calculate the enthalpy changes for the

            following reactions:

            (a) CH_4(g) + 2O_2(g) à CO_2(g) + 2H₂O_(g)

            (b) C₃H_8(g) + 5O_2(g) à 3CO_2(g) + 4H₂O_(g)

            (c) C₃H_6(g) + H_2(g) à C₃H_8(g)

            (d) N_2(g) + 2O_2(g) à 2NO_2(g)

 

4.        The production of hydrogen chloride from hydrogen and chlorine is exothermic.

H₂(g)   +   Cl₂(g)      →         2HCl(g)

Using bond enthalpy values, calculate the enthalpy change, in kJ mol^-1, for this reaction. 

5. Chloromethane can be produced by the reaction of methane with chlorine.

CH₄(g) + Cl₂(g) → CH₃Cl(g) + HCl(g)

Using bond enthalpies from the data booklet, calculate the enthalpy change, in

kJ mol⁻¹, for this reaction.