Exo- and Endothermic Reactions

1. Exo- and Endothermic Reactions Science 9

2. Energy Changes in Reactions • Every chemical reaction either uses energy or produces energy in the form of heat

3. Exothermic Reactions • Reactions that produce energy in the form of heat or light • “exo” means outside and “therm” means heat • The energy term written as a product • 2C2H2 + 5O2 4CO2 + 2H2O + energy

4. Exothermic reactions • Exothermic Reaction: a chemical reaction that releases energy into its surroundings • Often, chemical bond energy (when bonds are broken) is converted into heat energy • Reaction warms up its surroundings • Exothermic reactions can be extremely dangerous!!

5. Examples:

6. Exothermic reaction • Also includes changes of state • From Gasliquidsolid

7. Endothermic Reactions • Reactions that use heat energy • “endo” means inside and “therm” means heat • The energy term is written as a reactant • NH4NO3 + energy NH4+ + NO3-

8. Endothermic reactions • Endothermic reaction: a chemical reaction that absorbs energy from its surroundings • Chemical endothermic reactions need heat to be performed • Reaction cools down the surroundings (draws in heat, so feels cool)

9. Endothermic reactions • Examples: • Cooking food • Melting of ice • Photosynthesis • Changes of state: • From Solidliquidgas