C5 Flashcards
what is an exothermic reaction
a reaction which releases energy to the surroundings (usually as heat)
whats an endothermic reaction
a reaction that absorbs energy from the surroundings
what happens to the temperature in an exothermic reaction
it increases
give examples of exothermic reactions
combustion,neutralization,oxidation reactions
give examples of endothermic reactions
thermal decomposition, reaction of citric acid and sodium hydrogen carbonate , photosynthesis
whats activation energy
the minimum amount of energy needed for a reaction to start
whats the energy profile of an exothermic reaction
products have less energy than reactants:
energy is released
whats the energy profile of an endothermic reaction
products have more energy than reactants;
energy is absorbed
how is energy transferred in chemical reactions
through breaking and forming chemical bonds
is bond breaking exothermic or endothermic
endothermic
is bond forming exothermic or endothermic
exothermic
how can you calculate the overall energy change in a reaction
energy change= energy to break bonds-energy released when new bonds form
what does a negative energy change mean
the reaction is exothermic
what does a positive energy change mean
the reaction is endothermic
what is a reaction profile diagram
a graph showing the energy levels of reactants and products during a reaction
whats a simple cell
a device that converts chemical energy into electrical energy using 2 different metals in an electrolyte
what affects the voltage of a chemical cell
the type of metals used and the electrolyte
what is a battery
2 or more cells joined together to produce a higher voltage
what are non-rechargable batteries
batteries where the chemical reactions stop when one of the reactants is used up
what are rechargable batteries
batteries whereby the reaction can be reversed by passing an electrical current through them
whats a fuel cell
a cell that produces electricity using a continous supply of fuel and oxygen
whats the overall reaction in a hydrogen fuel cell
hydrogen+oxygen -> water
what are the advantages of hydrogen fuel cells
only waste product is water,efficient,no need to recharge
what are the disadvantage of hydrogen fuel cells
hydrogen is flammable,hard to store and often made using fossil fuels.
