Topic 5: energy changes Flashcards
what is the conservation of energy principle
energy is conserved in chemical reactions. the amount of energy.
what is exothermic reaction
a reaction where energy is transferred to the surroundings so that the surroundings temperature increases.
examples of exothermic reactions
combustion
oxidation reactions
neutralisation
acid and alkali reactions
what is an endothermic reaction
a reaction where energy is taken in from the surroundings so the surrounding temperature decreases
examples of endothermic reactions
thermal decomposition
reaction of citric acids and sodium hydrogen carbonate
what is activation energy
minimum amount of energy that particles need to react
what is a reaction profile
reaction profile is a graph which shows the relative energies of reactants and product, as well as activation energy of the reaction
what occurs in a chemical reaction in terms of bond energies
energy is supplied to break bonds and energy is released from forming bonds is greater than the needed to break the bonds; endothermic energy is needed to break bonds is greater than energy released in making them
what is the equation to find enthalpy change in terms of bond energies
energy of reaction = sum of bonds broken - sum of bonds made
what is a cell
a cell is composed of two electrodes dipped in an electrolyte solution, it produces electricity from a chemical reaction
what is a battery
a battery consists of two or more cells connected in series
what determines the voltage obtained from a cell
identifies of metals used as electrodes and the identify and concentration of an electrolyte
state the advantages of using cell and batteries
cheaper
some are rechargeable
a convenient source of electrical energy
a disadvantage of using cells and batteries
harmful chemicals
describe rechargeable cells
chemical reactions are reversed when an external current is supplied
