Energy Changes: Bond Energy Calculations

Question 1

What is meant by bond energies?

Answer 1

The amount of energy required to break 1 mole of a particular covalent bond.

Question 2

Is breaking bonds an endothermic or exothermic process and why?

Answer 2

Endothermic
It requires energy from the surroundings.

Question 3

Is forming bonds an endothermic or exothermic process?

Answer 3

Exothermic
It releases energy to the surroundings

Question 4

What formula would you use to calculate the overall energy change in a reaction?

Answer 4

Energy required to break bonds - energy released forming bonds

Question 5

If the value of the overall energy change in a reaction is negative, is the reaction endothermic or exothermic?

Answer 5

exothermic
energy has been lost to the surroundings

Question 6

If the value for the overall energy change energy change in a reaction is positive, is the reaction endothermic or exothermic?

Answer 6

endothermic
energy has been taken into the reaction from the surroundings

Question 7

Calculate the overall energy change in the following reaction. Is it endothermic or exothermic?

N₂ +3H₂ → 2NH₃

Answer 7

Energy required to break bonds = 2249
Energy released by forming bonds: 2346

Overal energy change = 2249 - 2346 =

-97kJ/mol

Exothermic

Question 8

How much energy is required to break the bonds in the following reaction?\

H₂ + Cl₂ → 2HCl

Answer 8

436 + 242 = 678kJ/mol