DF4- Bond Enthalpy

Question 1

Define bond enthalpy

Answer 1

Energy needed to break a particular bond in a molecule

Question 2

Why is bond enthalpy measured as an average?

Answer 2

Values change depending on molecule. Value is averaged over many different compounds

Question 3

Is bond breaking endo or exo thermic?

Answer 3

• endothermic; requires energy

- always positive

Question 4

Is bond making exo or endo thermic?

Answer 4

Exothermic- it releases energy

- always negative

Question 5

What are the steps you take to work out enthalpy change in a reaction?

Answer 5

1. Write balanced equation
2. Draw out molecules, displaying all bonds
3. Count bonds broken and made
4. Calculate enthalpy change using averages

Question 6

How is bond length linked to bond enthalpy?

Answer 6

• shorter bond length means there is more attraction between nuclei and shared electrons
• stronger the attraction, more energy needed to break bonds, higher bond enthalpy