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Energy in Chemical Reactions - Coggle Diagram
Energy in Chemical Reactions
Heat Changes in Chemical Reactions
Endothermic
temperature drop
heat taken in from surroundings
egs: sherbet and water, cold packs, photosynthesis
take in heat
Exothermic
heat lost to surroundings
give out heat
egs: neutralisation, burning, explosions, respiration, heat pads
temperature rise
Activation Energy
Collision Theory
molecules with high kinetic energies collide and products are formed
reaction particles MUST collide AND will only result in products if a certain MINIMUM energy is reached (= an effective collision
molecules with low kinetic energies collide and bounce apart without any reaction
Why are reactions faster at higher temperature
increased number of collisions as molecules are moving faster as they have more energy
i.e there are more effective collisions at higher temperatures
more of the colliding particles molecules have the minimum activation energy needed for reaction
Energy Profile Diagrams
small number of molecules have enough energy to pass energy barrier
rate is slow
large Ea - lots of energy must be supplied
rate is fast
small Ea - little energy must be supplied
large number of molecules have enough energy to pass energy barrier
why type of reactants affects the rate?
size of Ea depends on type of reactants
why particle size affects the rate?
smaller marble chips, more surface area exposed, number of collisions increases, therefore number of effective collisions increases, therefore rate increases
why concentration affects the rate?
increased concentration of reactants, molecules are closer together, therefore number of effective collisions increases, therefore rate increases
why does a catalyst affect the rate?
work by providing alternative route with a lower Ea, therefore more molecules have enough energy for an effective collision, therefore rate increases
