rate of reaction Flashcards
(17 cards)
rate equation
rate= k[A][B]
= K x [A]^m[B]^n
m+n = overall order for reaction
rate units= mol-1dm^3s^-1
k= rate constant
rate constant features
K
temperature dependent
different units for different reactions
- units of rate = conc/time
THE LARGER THE RATE CONSTANT THE FASTER THE REACTION
rate definition
change in concentration of a reactant or product over time
rate= gradient of a conc/time graph
RDS
slowest step in a reaction
- because it has the highest activation energy for a successful collision
RDS and reaction mechanism
reactants in the rate equation are involved in the rate determining step
- mechanism must involve them colliding at some point
collision theory
for a reaction to occur, particles must collide in the correct direction/ orientation and with enough energy (activation energy)
boltzmann distribution characteristics
starts at 0
total area under curve= total no. molecules
show only a very small proportion of particles have enough energy to react
boltzmann increased temp
shift right
higher proportion of particles have Ea (Ea in doesnt change)
peak lower and to right
flatter curve overall
why does increasing temp increase rate
larger proportion of molecules have activation energy
heat energy –> kinetic energy –> move more/ faster –>collide more frequently and with more energy –> more frequent, successful collisions
factors affecting rate
concentration
temp
pressure
catalyst
conc/ pressure on rate
increase= more frequent collisions as the particles are closer together so higher chance of reaction
catalysts on rate
increases rate of reaction by providing an alternative pathway for reaction with lower activation energy
benefit of catalysts
saves energy and money and time
lower temp required for reaction (lower Ea), therefore less heating = less emissions
less money required to heat for longer/ to higher temp
heterogeneous catalyst
in different phase/ state to reactants
eg. solid iron used in haber process with gaseous reactants
remains chemically unchanged at end of reaction
homogeneous catalyst
in same phase/ state as reactants
forms an intermediate during reaction but is then reformed at end
catalytic converters
in cars to reduce levels/ type of pollutants emitted
eg. CO/ NO2 -> CO2/ N2
ways to measure rate
iodine clock
loss of mass
disappearing cross
volume of gas produced
