1. During a science lab investigating chemical reactions, Mrs. Gray's students placed an antacid tablet in a zip lock bag. They recorded the mass of the tablet, 25 grams, and the bag, 60 grams. Then they carefully added 50 grams of water and quickly sealed the bag. The tablet began to fizz and soon disappeared. The bag was filled with gas. If the total mass of the bag + tablet + water was 135 grams before the reaction, what was the total mass of the bag + liquid + gas after the reaction was completed? 60 grams 75 grams 135 grams 270 grams

2. Exothermic vs Endothermic

3. Exothermic Reaction that transfers energy to the surroundings More energy is released when a bond forms than is used to break bonds Bond energy of the reactants is LESS than the bond energy of the products

4. Exothermic – Increase in temperature – Energy is released as heat and light REACTANTS PRODUCTS + ENERGY Examples: – Combustion reactions – Neutralization (acid/base) – Glow stick/Fireflies

5. Endothermic Reaction that takes in energy from the surroundings More energy is needed to break bonds in the reactants than needed to form bonds in the products Bond energy of the reactants is GREATER that the bond energy of the products

6. Endothermic Surroundings get colder Temperature decreases REACTANTS + ENERGY PRODUCTS Examples – Photosynthesis – Energy is stored as endothermic reaction; released as exothermic reaction

7. PHOTOSYNTHESIS 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2

8. Exo VS Endo Occurs in physical processes (changes) and chemical reactions

9. Physical Processes Closeness of the particles Endothermic: particles go from close together to far apart (takes energy) Melting, evaporation, boiling, sublimation

10. Physical Processes Exothermic: particles go from far to close (loses energy) Condensation; freezing