C5 Energy changes
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What happens in an exothermic reaction?
heat is transferred to the surroundings
what is an example of an exothermic reaction?
combustionneutralisation reactionsoxidation reactions- adding sodium to water
What products are exothermic reactions used in?
hand warmersself heating cans
what happens in an endothermic reaction?
heat is taken in from the surroundings
what are some examples of endothermic reactions?
citric acid and sodium hydrogencarbonatethermal decomposition- heating calcium carbonate for it to decompose into calcium oxide and carbon dioxide
what are some items that use endothermic reactions?
sports injury packs
what is the equation for thermal decomposition?
calcium carbonate + heat = carbon dioxide + quicklimecaco3 + heat = co2 + cao
How can we measure endo and exo thermic reactions?
taking the temperature of the reactantsmixing them up in a polystyrene cuptaking the temperature of the products
whats a problem with measuring energy change?
energy is lost to the surroundings
How can we reduce energy loss in a polystyrene cup?
putting it in a beaker of cotton wool to insulate it
what are reaction profiles?
diagrams that show relative energies of reactants and products
What is activation energy?
the initial energy needed to start the reaction
What is the reaction profile for an exothermic reaction?
reactants higher than productslittle blip of activation energy at the start
What is the reaction profile for an endothermic reaction?
products higher than reactantsactivation energy is total up
what happens to bonds during chemical reactions?
old bonds are broken and new bonds are formed
is bond breaking endo or exo?
endothermic- energy is needed to break the bonds
is bond making endo or exo?
exothermic- energy is released when new bonds are formed
An electro chemical cell is made up of 2 different electrodes in contact with an…………………..?
electrolyte
do reactants get used up in non rechargeable batteries?
yes