1. Endothermic & Exothermic Reactions

2. Endothermic process
Heat flows into the system from the surroundings in an endothermic process.
Surroundings
Cold pack
Energy
Temperature falls

3. Exothermic process
Heat flows into the surroundings from the system in an exothermic process.
Hot pack
Energy
Surroundings
Temperature rises

4. Energy Level Diagrams Endothermic reactions products reactants
energy taken in
is positive
reactants
The products are higher in energy than the reactants
time of reaction

5. Energy Level Diagrams Exothermic reactions reactants products
Energy given out
is negative
energy
reactants
products
Time of reaction
The products are lower in energy than the reactants

6. Exothermic reactions The products have less energy than the reactants.
The energy is given out to the surroundings.
The temperature goes up.

7. Endothermic reactions
The products have more energy than the reactants.
The energy is taken in from surroundings.
The temperature goes down.

8. But we use the unit called the JOULE
Units of Energy
James Joule
1 calorie = heat required to raise temp. of 1.00 g of H2O by 1.0 oC.
1 kcal = 1 Calorie (a food “calorie”)
But we use the unit called the JOULE
1 cal = joules

9. Breaking & Making Bonds
Breaking Bonds
always requires energy, so the process is endothermic
Making Bonds
gives off energy, so the process is exothermic

10. Energy (in Joules) CH4 + 2O2 CO2 + 2H2O C 4H 4O Step 1 Step 2
Step 1: Breaking Bonds (Endothermic)
Step 2: Making Bonds (Exothermic)