Calculating bond energy

Worked example 4

Bond breaking is an endothermic process. 

Bond making is an exothermic process. 


Overall energy change =  breaking bonds total energy –  making bonds total energy 

Worked example 4:

The reaction between methane and oxygen occurs as shown.

methane + oxygen --> carbon dioxide + water

CH4     +        2O2   -->    CO2   +        2H2O

The displayed formulae below show more clearly the bonds in each molecule involved in the reaction.

Calculate the total energy changes involved in the process of breaking and forming these bonds using the bond energies from the table below. (6)

Step 1. Calculate energy taken in when breaking bonds (1) 

(4 x C - H) + (2 x O = O)

(4 x 412) + (2 x 498) = 

Step 2. Calculate energy released from making bonds (1) 

(2 x C = O) + (4 x H - O) 

(2 x 805) + (4 x 464) = 

Step 3: Calculate total energy change (1) 

Overall energy change =  breaking bonds total energy –  making bonds total energy 

Overall energy change = 

Overall energy change =  kJ/mol 

Step 4: Explain if the reaction is an endothermic or an exothermic process. (3)

Overall energy change = kJ/mol