topic 5 energy changes
- Created by: Whitechoc10001
- Created on: 26-05-19 09:58
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- energy changes (topic 5)
- exothermic reactions
- transfers energy to its surroundings
- rise in temperature
- combustion (burning fuels)
- neutralisation reactions are often exothermic
- oxidation reactions
- hand warmers and self heating can of hot chocolate rely on exothermic reactions.
- bond making
- endothermic reactions
- releases energy into its surrounding
- decrease in temperature
- less common than exothermic reactions
- thermal decomposition
- sport injury packs
- bond breaking
- cells/batteries
- hydrogen-oxygen fuel cells
- electrolyte of potassium hydroxide, electrode of carbon
- anode
- hydrogen goes into the anode
- negative electrode (opposite to usual)
- hydrogen loses electrons to form H+
- hydrogen=> two hydrogen ions + two electrons
- cathode
- positive electrode
- oxygen gains electrons and reacts with H+ ions to form water
- oxygen + four hydrogen ions+four electrons=> two water molecules
- makes water
- advantages/ disadvantages
- not many pollutants
- don't need recharging
- cheaper
- more energy can be stored in them
- takes up a lot of space
- hydrogen is explosive so needs to be stored correctly
- normal cells
- system of two electrodes in contact with an electrolyte
- electrodes conduct electricity
- electrolyte contains ions to conduct electricity
- a cells voltage depend on difference in reactivity between electrodes
- magnesium is very reactive but copper isn't so its voltage would be high if used together
- if iron and zinc were used together, there would be a low voltage as they are similar in reactivity
- (non)rechargeable batteries
- the electrolyte gets turned back into reactants in a rechargeable batterie
- in non rechargeable batteries, the electrolyte gets used up
- system of two electrodes in contact with an electrolyte
- hydrogen-oxygen fuel cells
- exothermic reactions
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