8.2 [Bond enthalpy]

Question 1

What is bond enthalpy?

Answer 1

Bond enthalpy is the enthalpy change when one mole of a bond in the gaseous state is broken.

Question 2

What is meant by mean bond enthalpy?

Answer 2

That bond enthalpy of the C-H bond varies with its environment. It is often useful to quote mean bond enthalpy. For C-H the mean bond enthalpy is approximately 416kJ

Question 3

What is the process for calculating the enthalpy change of a reaction using mean bond enthalpies?

Answer 3

Step 1: Calculate the sum of the mean bond enthalpies of the bonds broken.
Step 2: Calculate the sum of the mean bond enthalpies of the bonds
Step 3: Calculate the enthalpy change of a reaction using the equation

Sum of the bonds broken - Sum of the bonds made

Question 4

What are the limitations of this method of calculation?

Answer 4

In some reactions there is a difference in the bond enthalpies that are measured in the gaseous state as some compounds are liquids