ENERGY CHANGES Flashcards
what happens to the energy in the universe?
doesn’t change, only moves around (energy is conserved)
what happens in an exothermic reaction?
transfers energy to surroundings by heating - heat is given out (temp increase)
examples of exothermic reactions?
combustion (burning fuels), neutralisation reactions and oxidation reactions
examples of exothermic reactions in everyday life?
hand warmers, self heating cans
what happens in an endothermic reaction?
takes in energy from surroundings (temp drop)
examples of endothermic reactions?
reaction between citric acid and sodium hydrocarbonate
thermal decomposition
examples of endothermic reactions in everyday life?
sports injury packs
PRACTICAL endo/exothermic reactions
- put 25cm3 of 0.25mol/dm3 of hydrochloric acid in a beaker
- do the same with sodium hydroxide
- put the beakers in a water bath set to 25
- put cotton in a larger beaker and place a polystyrene cup inside it (reduce energy lost)
- add the hydrochloric acid and sodium hydroxide to the polystyrene cup
- start a stopwatch immediately
- take the temp every 30s
- repeat using different concentrations of hydrochloric acid
what happens in chemical reactions, in terms of bonds?
old bonds are broken , new bonds are made
is bond breaking exothermic or endothermic?
endothermic - energy is supplied to break the bonds: energy used to break> energy released
why is forming bonds exothermic?
energy is released when making bonds: energy released>energy used to break
what are reaction profiles?
the diagrams to show the relative energies of reactants and products - show energy changes
describe the exothermic reaction profile.
starts from the top and reaches activation energy and drops to show the amount of energy released (reactants energy>products)
describe the endothermic reaction profile.
starts at the least amount of energy absorbed and increases to activation energy (products energy>reactants)
what is activation energy?
the amount of energy needed to break old bonds and start the reaction
