4.7- BOND ENTHALPIES

Question 1

If you plot ΔcH° against the number of carbon atoms in a molecule, for straight chain alkanes, what do you get?

Answer 1

straight line graph- suggests you can assign definite amount of energy to particular bond, called bond enthalpy

Question 2

What do you have to do to break a covalent bond?

Answer 2

put in energy

Question 3

What type of change is it when you put in energy to break a covalent bond?

Answer 3

endothermic change

Question 4

What is bond dissociation enthalpy defined as?

Answer 4

enthalpy change required to break covalent bond with all species in gaseous state

Question 5

What is the energy put in to break a covalent bond the same as?

Answer 5

same amount of energy given out when bond formed

Question 6

What type of change is it when energy given out when bond formed?

Answer 6

exothermic change

Question 7

How have mean bond enthalpies been calculated?

Answer 7

using Hess’s law cycles