Exothermic and Endothermic Reactions

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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

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Energy level diagramsEnergy level

Reaction progress

Activation energy

Energy given out

by reactionUsing a catalyst might lower the

activation energy

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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 HeatMeasuring Heat

reaction

Endothermic Endothermic reaction, heat reaction, heat

taken in & taken in & temperature of temperature of the substance the substance

dropsdrops

Ammonium nitrate + water

Starting temperature 20 C⁰

Add ammonium nitrate to water

a temperature decrease of 8 C⁰

EXOTHERMIC & ENDOTHERMIC REACTIONSEXOTHERMIC & ENDOTHERMIC REACTIONS

Exothermic process: a change (e.g. a chemical reaction) that releases

heat.

Burning fossil fuels is an exothermic

reaction

Heat Released

Exothermic Exothermic reaction, heat reaction, heat

given off & given off & temperature of temperature of

substance substance rises.rises.

reaction

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

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