Endothermic & Exothermic Reactions

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

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

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

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

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

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

But we use the unit called the JOULE Units of Energy James Joule 1818-1889 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 = 4.184 joules

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

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