C5/Energy Changes Flashcards
what happens to energy in chemical reactions?
energy is conserved
the amount of energy in the universe at the end of a chemical reaction is the same as what?
it is the same as before the reaction takes place
an exothermic reaction is one of that transfers energy where?
to the surroundings, so the temperature of the surroundings increases (a heat is given out)
give examples of exothermic reactions
combustion
many oxidation reactions
neutralisation
give some everyday uses of exothermic reactions
self-heating cans
hand warmers
an endothermic reaction is one that transfers energy where?
it takes energy from the surroundings, so the temperature of the surroundings decreases (as heat is taken in)
give examples of an endothermic reaction
thermal decompositions
reaction of citric acid and sodium hydrogencarbonate
give an everyday use of an endothermic reaction
sports injury packs
chemical reactions can occur only when reacting particles collide with each other and with sufficient what?
energy
the minimum amount of energy that particles must have to react is called with?
the activation energy
what type of diagram can be used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction?
reaction profile diagram
during a chemical reaction energy must be supplied to break the bonds in what?
in the reactants
during a chemical reaction energy is released when bonds in the products are what?
when bonds are formed
what can be calculated from the energy needed to break bonds minus the energy released when bonds are formed?
the bond energies
the difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed is called what?
the overall energy change of the reaction
in what type of reaction is the energy released from forming new bonds greater than the energy needed to break existing bonds?
in an exothermic reaction
in what type of reaction is the energy needed to break existing bonds is greater than the energy released from forming new bonds?
in an endothermic reaction
cells contain chemicals which react to produce what?
electricity
the voltage produced by a cell is developed upon a number of factors.
name 2 of these.
the type of electrode
the type of electrolyte
describe how a simple cell can be made (battery)
by connecting two different metals in contact with an electrolyte
batteries consist of what?
two or more cells connected together in series to provide a greater voltage
in non-rechargeable batteries and cells the chemical reactions stop when what happens?
one of the reactants has been used up
name a non-rechargeable type of battery
alkaline batteries
rechargeable batteries and cells can be recharged because the chemical reactions are reversed when what is supplied?
when an external electrical current is supplied
fuel cells are supplied by an external source of fuel and what?
oxygen or air
what happens to the fuel within the fuel cell when it produces a potential difference?
it is oxidised electrochemically
the overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce what?
water
hydrogen fuel cells offer a potential alternative to what?
rechargeable cells and batteries
