t5-energy changes Flashcards
what is the conservation of energy
energy is conserved in reactions so the amount of energy at the start and end of a reaction is the same
what is an exothermic reaction
give examples
a reaction where energy is transferred to the surroundings so the surrounding temperature increases
eg.combustion, oxidation reactions and neutralisation
has a negative sign of energy change
what is an endothermic reaction
give examples
a reaction where energy is taken in from surroundings so the surround temperature decreases
eg.thermal decompostion
positive sign of energy change
what is activation energy
minimum amount of energy needed for particles to react
what is reaction profile
graph to show the activation energy and the relative energies of reactants and products
what occurs in a chemical reaction in terms of bond energies in exothermic/endothermic reactions
exothermic-energy is supplied to break bonds and energy is released when bonds are made
endothermic- the energy released when forming bonds is greater than that needed to break the bonds
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
produces electricity from a chemical reaction
what is a battery
consists of 2 or more cells connected in series
what determines the voltage obtained from a cell
identities of metals used as electrodes and the identity and concentration of the electrolyte
what is are 3 advantages of using cells and batteries
cheap
some are rechargeable
convenient source of electrical energy
what is a disadvantage of using cells and batteries
harmful chemicals
what is a rechargeable cell
chemical reactions are reversed when an external current is supplied
what is a non rechargeable cell
reactants are used up
what is a fuel cell
supplied by fuel and oxygen to oxidise the fuel to generate electricity
