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

Energy level diagrams Energy level Activation energy Using a catalyst might lower the activation energy Energy given out by reaction Reaction progress © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

Forming Na+ and Cl- ions from NaCl is an endothermic process 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)

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

Ammonium nitrate + water

Starting temperature 20⁰ C

Add ammonium nitrate to water

a temperature decrease of 8⁰ C

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

Exothermic reaction, heat given off & temperature of substance rises. Heat Released reaction Exothermic reaction, heat given off & temperature of substance rises.

Exothermic vs endothermic: EXOTHERMIC – 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 Exothermic Combustion of fuels Yeast & Hydrogen Peroxide Epson salts & water Endothermic Photosynthesis Acedic Acid & Sodium Bicarbonate © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910