5.3 Bond Enthalpy

The complete combustion of ethyne, C₂H₂, is shown in the equation below. 

H−C≡C−H + 2½ O═O  →  H−O−H + 2O═C═O 

Using the average bond enthalpies given in the table, what is the enthalpy change of combustion of ethyne?

Compound R into compound T, it was found that the reaction proceeded by way of compound S, which could be isolated. The following steps were involved. 

R → S;  ΔH is positive

S → T; ΔH is negative

Which reaction profile fits these data?

The reaction pathway for an endothermic reaction is shown.

 Which arrow represents the activation energy for the reverse reaction?

The reaction pathway shows the energies of the reactants, the products and the transition state of a reaction.

Which expression correctly represents how to calculate the activation energy of the forward reaction?

The incomplete combustion of methanol can produce carbon monoxide and water: 

Some enthalpy data is given in the table.

What is the enthalpy change for this incomplete combustion of methanol?

Which of the following statements about bond enthalpy are true? 

1. A bond enthalpy may be inaccurate when compared to data tables because it is not an average value
2. Average bond enthalpies are valid for all states of matter
3. Bond enthalpies may be inaccurate as they do not account for intermolecular forces

Four possible reactions (A, B, C and D) of the following equation are measured at the same temperature. 

                                                X (g) + Y (g) → Z (g) 

Which reaction pathway diagram shows the reaction occurring rapidly with an overall negative enthalpy value?

Which combination about bond breaking and bond formation energy changes is correct?

Which reactions are involved in maintaining the concentration of ozone in the upper atmosphere? 

1. O₃ → O₂ + O^●
2. O₂ → 2O^●
3. O₂ + O^● → O₃