Rates Flashcards
Rate of reaction
How fast a reactant is being used up/product is being formed
Rate=change in conc/time
Fastest at start highest conc of reactant
Effective collision theory
2 reacting particles must collide with the correct orientation and sufficient energy in order for a reaction to occur
Catalyst
Substance that changes the rate of reaction without undergoing permanent change itself
Provides alternative pathways w lower activation energy
Enthalpy profiles
Endothermic reactants lower than products (enthalpy arrow up)
Exothermic reactants higher than products (enthalpy arrow down)
Homogenous catalyst
Same physical states as reactants
Forms an intermediate which breaks down to give the product and regenerates the catalyst
Eg sulphuric acid making an ester
Or Cl • radicals in ozone
Heterogenous catalysts
Different physical state from reactants
Reactant molecules are adsorbed onto surface
Products desorped
Eg Fe in haber process
No in hydrogenation of Alkene
Catalyst importance
Less fossil fuel is used making product faster w less energy increase profitability
High atom economies and fewer pollutants enzymes do this cutting co2 emissions due to less energy required
Boltzmann distribution curves
No molecules have zero energy curve starts at origin
Are under curve is equal to total number of molecules
Doesn’t touch x axis - no maximum energy
Temp x Boltzmann
At higher temp peak is lower and shifted to the right greater proportion can overcome activation energy
Catalyst x Boltzmann
Alternate route lowering the activation energy - greater proportion of molecules (closer to y axis)
Dynamic equilibrium
When the rate of the forward reaction is equal to the rate of the backwards reaction
Conc of products/reactants don’t change
Must occur in a closed system
Le Chatelier’s principle
When a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change
Conc x equilibrium
If more products equlibrium shifts to the left
If more reactants equilibrium has shifted to the right
Temp x equilibrium
Increase in temp shifts equilibrium in endothermic direction
Decrease in temp shifts equilibrium in Exothermic direction
Equilibrium constant
Kc = products / reactants
(Number of moles = power of)
