Calculating energy changes

Calculating energy changes

1. Exothermic reactions give out heat

2. If the energy given out is more than it needs to break the bonds the reaction is exothermic.

3. Endothermic reaction take in heat

4. Energy change= Total energy needed to break all bonds-total energy given out when new bonds are formed

5. Example CH4 + 2O2----> CO2 + 2H20

6. 4*C-H=(4*412)=1648kj

7. 2*O=O =(2*496)=992kj

8. Total energy in = 2640kj

9. Bonds formed are C=O and O-H

10. 2*C=O =(2*743)=1486kj

11. 4* O-H =(4*463) =1852kj

12. Total energy out=3338kj

13. Total energy change= 2640-3338=-698kj

    • Exothermic reaction