Calculating the enthalpy of reaction from bond energies
Three steps are involved:
  1. Calculate the energy needed to break the bonds in the reactant molecules, Hr.
  2. Calculate the energy released in the making of new bonds in the product molecules, Hp.
  3. Calculate the sum of the two totals, Hp + Hr.

Have a go! Use the data from the table right (top) to enter values in the boxes in the green area. Ensure you get the signs correct. Press RESULT to calculate the enthalpy of reaction  and to see how many entries were correct.

Questions imageIs this reaction an exothermic or an endothermic reaction?

Have a go! Try other self assessment exercises:

H2(g) + Cl2(g) ® 2HCl(g)

2H2(g) + O2(g) ® 2H2O(g)

N2(g) + O2(g) --> 2NO(g)

Bond Bond energy
(kJ mol-1)		 Bond Bond energy
(kJ mol-1)
C-C 346 H-H 436
C-O 358 N-H 391
O-H 46 NºN 946
O=O 498 N=O 631
H-Cl 431 Cl-Cl 242
H-H 436    
Bond breaking Bond making
Nitrogen

Nitrogen(II) oxide

Moles nitrogen

Moles nitrogen(II) oxide

Oxygen

   

Moles oxygen

   

Enthalpy =  x + x + x

= kJ mol-1

Score =

 

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