Exothermic and Endothermic Reactions TP: Explore and explain the idea of endothermic processes and exothermic reactions. © Teachable. Some rights reserved.

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.

Energy level diagrams Energy level Reaction progress Activation energy Energy given out by reaction Using a catalyst might lower the activation energy © Teachable. Some rights reserved.

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

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

Ammonium nitrate + water

Starting temperature 20 ⁰ C

Add ammonium nitrate to water

a temperature decrease of 8 ⁰ C

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

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

Endothermic Reactions Endothermic reactions are reactions which take energy in from their surroundings. If a substance is undergoing an endothermic reaction would it’s surroundings get warmer or colder? It’s surroundings get colder. Endothermic reactions occur when the bonds of a substance are being broken.

Useful Endothermic Reactions When things dissolve they are undergoing an endothermic reaction. Cooking is an endothermic reaction. –The food takes in the heat provided by the cooker. –The chemicals of the food undergo a chemical reaction which makes them easier to digest. Cold packs for sports injuries rely on endothermic reactions. –When you twist or shake the pack the chemicals in the pack start reacting. –Because they undergo an endothermic reaction they take heat in from their surroundings. –This makes the pack cold.

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.

Exothermic Reactions Exothermic reactions give off heat. They occur when chemical bonds are formed. If substances are undergoing exothermic reactions will their surroundings get hotter or colder? The will get hotter.

Useful Exothermic Reactions Combustion: all combustion reactions give off heat. Neutralization reactions are exothermic. Hot Pad hand warmers –When the hand warmer is shaken they chemicals inside undergo an exothermic reaction –This releases the heat which helps to warm up your hand. Self heating coffee cans. –When the tab is popped chemicals mix together and an exothermic reaction occurs. –This releases heat which warms up your coffee. –The chemicals are kept separate from the coffee

Examples Exothermic Combustion of fuels Yeast & Hydrogen Peroxide Epson salts & water Endothermic Photosynthesis Acedic Acid & Sodium Bicarbonate © Teachable. Some rights reserved.

Define and draw an picture to illustrate: Exothermic Endothermic Thermal (heat) Energy transfer Conduction Convection Radiation Evaporation.