Transcript Exothermic and Endothermic Reactions
Exothermic and Endothermic Reactions
TP: Explore and explain the idea of endothermic processes and exothermic 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
Energy level diagrams
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
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
Endothermic reaction, heat taken in & temperature of the substance drops reaction
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
Heat Released reaction Exothermic reaction, heat given off & temperature of substance rises.
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 endothermic reaction.
they are undergoing an • 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) © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910 ENDOTHERMIC – energy is taken in but not necessarily given out (e.g. photosynthesis)
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
Exothermic
Examples
Endothermic
• Combustion of fuels • Yeast & Hydrogen Peroxide • Epson salts & water • Photosynthesis • Acedic Acid & Sodium Bicarbonate © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910
Define and draw an picture to illustrate: • Exothermic • Endothermic • Thermal (heat) • Energy transfer • Conduction • Convection • Radiation • Evaporation .