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4b: Energetics (exothermic reactions (GIVE OUT energy, heat is detected as…
4b: Energetics
exothermic reactions
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as the reaction progresses, energy is released in the form of heat
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e.g. in an equation this is shown as
Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g) △H= -467KJ mol-1
this equation tells us that when magnesium reacts with sulfuric acid, the overall energy change △H is -467 KJ mol-1
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activation energy
what it is = the minimum energy required to start a reaction. It may be reduced by using a catalyst, which provides an alternative route for the reaction
energy level exothermic
energy level endothermic
activation energy - provides extra energy to break bonds between reacting mass (endo). Atoms then make the products i.e. make bonds (exo)
energy level diagrams
exothermic
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- for all exothermic reactions, △H is always negative
- the heat is transferred to the surroundings which then get warmer
- units of △H are KJmol-1 (kilojoules per mole)
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key terms:
exothermic = give out energy
endothermic= absorb energy
reactants=substances you put into a reaction
products=substances you get out of a reaction