Energy Changes Flashcards
Hos much overall amount of energy is present after a reaction.
It doesn’t change -energy is conserved. It neither be created nor destroyed only moved around
What happens during an exothermic reaction
Provide examples and everyday uses
Releases energy towards the surroundings usually by heating (temp increase)
Burning fuels-combustion
Neutralisation reactions- (acid + alkali)
Oxidation reactions (sodium and water)
Hand warmers and self heating cans
What happens during an endothermic reaction
Provide examples and everyday uses
Absorbs energy from the surroundings. Fall in temperature
Reaction of citric acid and sofium hydrogencarbonate
Thermal decomposition
Sports injury pscks
Required practical: measuring energy transfer
1) Equipment needed
1) Polystrene cup, thermometer,lid, beaker, reaction mixture,cotton wool
2) Put 25cm3 of 0.25mol/dm3 Hcl and sofium hydroxide in seperste beakers
3) place beakers inside a water bath at 25°c and take them out at the same time
4) Add the hcl followed by the NaOH to the polystrene cup in the beaker and cover it with a lid
5) Take the temperature of the mixture every 30 seconds and record highest temp
6) Repeat steps 2-5 using 0.5mol/dm3 and 1mol/dm3
How does a reaction profile show exothermic and endothermic reaction
Exothermic reaction: products at a lower energy level then the reactants.
Height difference represents the energy release
Reactants to peak = activation energy
Endothermic reactions: products greater than the reactants
Height difference represents enrgy absorbed
Reactants to peak = activation energy
What is activation energy
Activation energy is the mininum amount of energy required for the reactants to start a reaction.
Bond energies in endothermic and exothermic reactions
Exothermic reaction: energy released forming bonds greater then energy used to break them
Endothermic reaction: Energy used ro break bonds greater then energy released forming them
