Exothermic and Endothermic Reactions © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

Endothermic and Exothermic Reactions Step 1: Energy must be SUPPLIED to break chemical bonds: Step 2: Energy is RELEASED when new chemical bonds are made: A reaction is EXOTHERMIC if more energy is RELEASED than SUPPLIED. If more energy is SUPPLIED than is RELEASED, then the reaction is ENDOTHERMIC. © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

Forming Na+ and Cl- ions from NaCl is an endothermic process a change (e.g. a chemical reaction) that requires (or absorbs) heat. Forming Na+ and Cl- ions from NaCl is an endothermic process Photosynthesis is an endothermic reaction (requires energy input from sun.)

heat taken in & temperature of the substance drops Measuring Heat reaction Endothermic Reaction- heat taken in & temperature of the substance drops

Example: Ammonium nitrate + water

The starting temperature is 20⁰ C.

Add ammonium nitrate to water

The temperature decreased by 8⁰C and is now registering at 12⁰C.

EXOTHERMIC & ENDOTHERMIC REACTIONS Exothermic process: a change (e.g. a chemical reaction) that releases heat. Burning fossil fuels is an exothermic reaction

heat given off & temperature of substance rises. Heat Released Measuring Heat reaction Exothermic Reaction- heat given off & temperature of substance rises.

Exothermic vs Endothermic: more energy is given out than is taken in (e.g. burning, respiration) ENDOTHERMIC – energy is taken in but not necessarily given out (e.g. photosynthesis) © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

Examples Endothermic Photosynthesis Baking bread Evaporation of water Cooking an egg Melting ice cubes Exothermic Combustion of fuels Candle flame Rusting iron Formation of snow in clouds Making ice cubes © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910