Exothermic & Endothermic
Reactions
Name: _______________________
Date: ____________________
Block: _______
Energy in Reactions
Some chemical reactions release heat to the surroundings

These are called ______________________ reactions

Some chemical reactions absorb heat from the surroundings

These are called ______________________ reactions.

All substances have a type of chemical potential energy stored within them.
ENTHALPY:
 The total energy (J or kJ) contained in a system

Chemical potential energy in a substance

The symbol for enthalpy is H

_______________________________________
Exothermic Reactions
An exothermic reaction converts the enthalpy stored in a substance into HEAT which is _______________________ to
the surroundings
N2 + 3 H2 
The reaction above can be shown on a graph.
2 NH3 + heat
Enthalpy (H)
There are two ways to show that a reaction is exothermic:
1. The “heat term” written on the _______________________ side.
2. ΔH written beside the equation is _________________________.
Reaction Proceeds
To summarize, in an exothermic reaction:



Endothermic Reactions
An endothermic reactions _____________________ heat from the surroundings and converts it into enthalpy
2C + 2 H2 + heat  C2H4
The reaction above can be shown on a graph.
Enthalpy (H)
Reaction Proceeds
There are two ways to show that a reaction is endothermic:
1. 1. The “heat term” written on the _______________________ side.
2. ΔH written beside the equation is _________________________.
To summarize, in an endothermic reaction:



Practice Questions - Student
State whether each of the following are exothermic or endothermic.
1. H + Cl  HCl + 432 kJ
2. 12 CO2 + 11 H2O  C12H22O11 + 12 O2
ΔH=5638 kJ
3. ice  water
4. C + D  CD
ΔH=-65.8 kJ
5. E + F + 437 kJ  G + H
6. H2O vapour  H2O liquid
7.
Practice Questions - Teacher
State whether each of the following are exothermic or endothermic.
1. Exo
1. H + Cl  HCl + 432 kJ
2. 12 CO2 + 11 H2O  C12H22O11 + 12 O2
ΔH=5638 kJ
3. Endo
3. ice  water
4. C + D  CD
5. E + F + 437 kJ  G + H
6. H2O vapour  H2O liquid
2. Endo
ΔH=-65.8 kJ
4. Exo
5. Endo
6. Endo
7. Exo
7.