Exothermic and Endothermic Reactions Flashcards
Energy is conserved in chemical reactions so the total amount of energy in the universe after a reaction is….
….the same as it was before the reaction.
Exothermic reaction
-when energy is transferred to the surroundings
-temperature of the surroundings increases
Examples of exothermic reactions:
-combustion reactions
-oxidation reactions
-most neutralisation reactions
What is a combustion reaction?
-process of burning by heat
What is an oxidation reaction?
-gain of oxygen, or loss of electrons, by a substance, during a chemical reaction
What is a neutralisation reaction?
-reaction between an acid and a base to form a salt + water
Everyday uses of exothermic reactions include…
…self-heating cans and hand warmers
Endothermic reactions
-when energy is taken in from the surroundings
-temperature of the surroundings decreases
Examples of endothermic reactions:
-thermal decomposition reactions
-photosynthesis
What is a thermal decomposition reaction?
-where a compound breaks down to form two or more substances when heated
Everyday uses of endothermic reactions include…
…instant ice packs to treat sports injuries
There is an energy transfer in chemical reactions when…
…bonds between atoms and ions are formed or broken
Activation energy
-the minimum amount of energy particles must have to react
Why does the energy level decrease in an exothermic reaction?
-energy is released in order to form bonds
Why does the energy level increase in an exothermic reaction?
-energy is taken in to break bonds
Describe how you can tell from a reaction profile that a reaction is exothermic
-overall change is negative
-products have less energy than the reactants
-arrow showing the overall change in energy points downwards
Describe how you can tell from a reaction profile that a reaction is endothermic
-overall change is positive
-products have more energy than the reactants
-arrow showing the overall change in energy points upwards
If more heat energy is released in making bonds in the products than is taken in when breaking bonds in the reactants, the reaction is….
…exothermic
If less heat energy is released in making bonds in the products than is taken in when breaking bonds in the reactants, the reaction is….
…endothermic.
Method to calculate an energy change for a reaction
-add together the bond energies for all the bonds in the
reactants
(this is the ‘energy in’)
-add together the bond energies for all the bonds in the
products
(this is the ‘energy out’)
-energy change = energy in - energy out
