Chemistry 2: Rate & Extent of Chemical change
Collision theory & Activation energy
Activation Energy:
Minimum energy needed for particles to react
Frequency of collisions can be increased by:
Collision Theory:
Particles need to collide with enough energy to react
Increase concentration of reactants
Increase Pressure
Increased SA
Increase temperature
Rate of reaction:
Units for Rate of Reaction:
Cm3/s or G/s or Mol/s
3 Ways to measure Rate of R:
Mean rate of reaction = amount of reactant used (or product formed) ÷ time
• Precipitation/colour change
• Change in mass
• Volume of gas given off
Factors affecting
the rate of chemical reactions
Catalysts
Five factors:
Temperature
Surface area of a solid
Concentration of a solution
Pressure in a gas
Catalyst presence
Catalyst increases the rate of reaction:
- Catalysts decrease activation energy needed
- Provide a different reaction pathway
Catalyst is?
- Substance that speeds up a reaction
- Doesnt get used
Reversible reactions
& Energy changes:
Reversible reaction:
The reaction can be reversed to produce the original reactants
Energy changes in R-R:
One way is EXO, other is ENDO
-- Same amount of energy is transferred either way
Equilibrium:
Le Chatelier's Principle:
To predict the effect of changing th conditions of a system at equilibrium
Concentration:
Equilibrium is...
The rate of the forward reaction = the rate of the reversed one
Increase Conc' of reactants...
More products will be formed - Until Equil is reached
(Vise versa w/ Products)
If Concentration (At Equil') changes:
- System will no longer be Equal
- So the Conc' will change - Until Equil' is reached again.
Effect of Temp / Pressure
On Equilibrium:
Temp:
Pressure:
Temp increase = Endothermic
Temp decrease = Exothermic
Increase pressure = Least num of molecules
Decrease pressure = More num of molecules