Energy changes - Chemical and fuel cells

a basic system made up of two different electrodes in contact with an electrolyte

conduct electricity

• difference in reactivity of the two electrodes, the higher the difference between them, the bigger the voltage of the cell • the electrolyte as different ions in the solution will react differently with the metal electrodes used

by connecting two or more cells together in series

batteries where the reactants get used up- e.g an alkaline battery

• irreversible • over time, the reacting particles get used up and turn into the product of the reaction • once any one of the reactants get used up, the reaction can’t happen, no electricity produced • products cant be turned back to reactants, so the cell cannot be recharged

a cell where the chemical reaction can be reversed by connecting it to an external current - e.g a phone or laptop battery

an electrical cell thats supplied with fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently

a fuel cell which combines hydrogen and oxygen to produce clean water and releases energy

• involves a redox reaction • hydrogen goes to the anode (oxidation as it loses electrons ), oxygen to the cathode ( reduction • at the cathode, oxygen gains electrons from the cathode and reacts with the H+ ions to make water ( reduction)

• don’t produce as many pollutants as other fuels, only by- products are water and heat • better than electric vehicles as their batteries are polluting to dispose of • less charging time than electric cars as they store more energy • electric car batteries are more expensive to make then fuel cells

• hydrogen is a gas so takes more space to store than a rechargeable battery • hydrogen is explosive when mixed with air, harder to store • the hydrogen fuel is made from hydrocarbons which use electricity which come from fossil fuels

O2 + 4H+ + 4e»_space;»2H2O reduction

2H2 + o2 —-2H2O

by taking 2 metals of different reactivity and placing them in an electrolyte

a solution that can conduct electricity - eg, the solution of an ionic compound

• a cell can only produce electricity for a certain period of time, eventually, the chemicals in the cell run out and the reaction stops • cells only produce electricity when metals of different reactivity are used

chemicals which react to produce electricity

f two or more cells connected together in series which produces greater voltage

a solution that can conduct electricity

• react a fuel such as hydrogen with pure oxygen or air • inside the fuel cell, a chemical reaction takes place, producing an electric current • only waste product is water

• hydrogen molecules split into hydrogen ions and electrons • 2H2 —> 4H+ +4e

• oxygen molecules combine o2 + 4H+ 4e - —> 2H2o

2H2 + O2 —-> 2H2O