Topic 5- Energy Changes. Flashcards
what do different chemicals store?
they store different amount of energy.
what do products of reaction sometimes store?
they can sometimes store more energy than the reactants. this means that the products have taken in energy from the surroundings during the reaction.
what happens if products store less energy?
then the extra energy was transferred to the surroundings during the reaction.
what is the amount of energy transferred the difference between?
it is the difference between the energy of the products and the energy of the reactants.
what doesn’t change overall?
the overall amount of energy doesn’t change. energy stays the same in reactions. it can’t be made, changed or destroyed. it can only be moved around.
what is an exothermic reaction?
it is when energy is given out to the surroundings. it is shown by a rise in temperature.
examples of exothermic reaction?
- burning fuels- combustion.
- neutralisation reactions- acids and alkalis.
what are the everyday uses for exothermic reactions?
- hand warmers.
- self-heating cans.
what is an endothermic reaction?
it is when it takes in energy from the surroundings. this is shown by a fall in temperature of the surroundings.
examples of endothermic reaction?
- reaction between citric acid and sodium hydrogencarbonate.
- thermal decomposition- substances break down when heated.
what are the everyday uses of endothermic reactions?
- sport injury packs.
- instant coolers.
what is the activation energy?
it is the minimum amount of energy the reactants need to have to react when they collide with each other. the greater the activation energy, the more energy is needed to start the reaction. energy has to be given.
what do reaction profiles show?
they show the energy changes. they are diagrams that show differences between the energies of the reactants and the products and how the energy changes over the course of the reaction.
what is the reaction profile like for exothermic reactions?
- products are at a lower energy then the reactants.
- difference in height between the reactants and the products - overall energy change in reaction, the energy is given out.
- rise in energy at the start shows the energy needed to start the reaction- the activation energy.
what is the reaction profiles like for endothermic reaction?
- products are a higher energy than the reactants.
- difference in height shows the overall energy change during the reaction (energy taken in).
