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the breaking of bonds in a chemical reaction which requires energy (on the reactants side)
energy absorbed from surroundings is stored up as potential energy in the system (+)
the formation of bonds in a chemical reqction which releases energy (on the products side)
potential energy in the system is released as heat to the surroundings (-)
average bond enthalpy
the energy needed to break one mole of covalent bonds between atoms in the gas state
specific heat capacity
amount of heat needed to raise the temperature of 1 gram of a substance by 1 degree Celcius
when several reactions can be added to give one overall reaction, the enthalpy change for the overall reaction is the sum of the enthalby change for the individual reactions
- reverse a reaction, reverse the enthalpy sign
- if you need to multiply a reaction, multiply it's enthalpy with the same number
- particles must have sufficient energy (activation energy - Ea)
- particles must collide in the correct orientation
more effective collisions = faster reaction
Decomposition of Hydrogen Peroxide
2H2O2 --> (MnO2) 2H2O + O2
manganese oxide (i.e. manganese dioxide) is the catalyst
rate determining steps (RDS)
the slowest step in the mechanism; the overall reaction cannot go any faster than this step
the rate of the forward reaction equals the rate of the reverse reaction in a closed system (concentrations are constant but not equal)
indicates the "extent" of the reaction
- large Keq means there are more products than reactants
- very large Keq means the reaction goes to completion
- small Keq means there are more reactants than products
- affected by temperature
Le Chatelier's Principle
when a stress is applied to a reaction at equilibrium, the reaction shifts left or right to relieve the stress and establish a new equilibrium
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