Topic 5: Energetics 5.1 Exothermic and endothermic reactions 5.2 Calculation of enthalpy changes.
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Transcript of Exothermic and Endothermic Reactions © Teachable. Some rights reserved. .
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 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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