1.5.1 &1.5.2: Reaction Rates and catalysts Flashcards
Rate of reaction
equation
amount of reactant used or product formed/ time
Reaction rate
Change in concentration (or amount) of product or reactant over time
Particles must … to react
3
collide
have sufficient energy (Ea)
collide with correct orientation
Activation energy
Minimum amount of kinetic energy particles need to react
Molecules in a gas
have different amounts of kinetic energy
Graph of no. of molecules vs kinetic energy
Maxwell-boltzmann distribution
Factors that affect rate of reaction
4
temperature
concentration
pressure
presence of a catalyst
How temp affects rate of reaction
Particles on average have high kinetic energy
move faster
greater proportion of molecules have activation energy
also collide more often
pushes curve to right
Temp affect on ROR
small increase in temp = large increase in ROR
How conc affects ROR
increase conc = particles on average closer together = collide more often = more chances to react
How pressure affects ROR
(gas)
particles closer together = more likely to collide and more frequent collisions
increased ROR with pressure increase
Catalyst
A substance that increases the rate of the reaction by providing an alternative reaction pathway with a lower activation energy whilst remaining chemically unchanged
Ways to measure reaction rates
3
time a precipitate takes to form
measuring a decrease in mass
measuring the volume of gas given off
example of experiment involved with rates of reaction
Sodium thiosulphate and hydrochloric acid
disappearing cross experiment
Stenic factor
Location of a collision matters
Activation energy
role
breaks bonds in reactants so new bonds can form in products
Most collisions…
don’t result in a reaction
Curve for distribution of energies
Maxwell-Boltzmann
Maxwell-Boltzmann curve
area under graph
total number of molecules
Maxwell-Boltzmann curve
asymptotic
means
tends to 0 but doesn’t touch the x axis
small possibility of a very high energy molecule
Maxwell-Boltzmann curve
molecules energy
no molecules have 0 energy
Maxwell-Boltzmann curve
curve passes through
origin at (0,0)
Maxwell-Boltzmann curve
Peak
(the middle)
most molecules with certain energy
most likely energy
Maxwell-Boltzmann curve
average energy
right of max/peak
