6 chemical kinetics
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define chemical kinetics
the study of factors affecting the rate of a chemical reaction.
what is the rate of a chemical reaction
the increase in concentration of one of the products per unit time or as the decrease in the concnetration of one of the reactants per unit time
what is rate of reaction measured in
mol dm^-3 s^-1
how can you measure change in conc
using any property that differs between the reactants and products. mass or volume changes absorption using a spectrometer when there is colour change pH changes when there is a change in acidity electrical conductivity when there is a change in ionic concentrations.
what do you do with data (from a data logger) about a a change in conc
a graph is plotted (concentration against time) rate at any stated point in time is then the gradient of the graph at that time. rates of reaction usually decrease with time as the reactants are used up
what is a maxwell boltzmann curve
the distribution of kinetic energies. number of particles (y) vs kinetic energy (x)
would a high temperature have a high y value or low on the maxwell boltzmann curve
lower, as the curve would broaden, as the increase of kinetic energy is counted on the x axis.
how to find rate of reaction from a graph
change in time (x)
when a rate of reaction graph line goes flat what does it mean
the reaction has gone to completion
for particles to have a reaction, what 3 requirements need ot be met
particles must collide they must collide in the correct orientation. must collide with sufficent energy to bring about the reaction.
what is the minimum amount ofenergy required for a reaction to occur called
activation energy
factors affecting rate of reaction
temperature surface area concentration catalyst
how does temperature increase rate of reaction
particles move faster more collisions per second particles will have gained KE, and consequently more will reach activation energy.
an increase of about 10 degrees celsius
doubles rate of reaction ROUGHLY
how does surface area increase rate of reaction
in a solid, only particles on the surface can come into contract with a surrounding reactant, so increasing the surface area allows more to be in contact, increasing number of collisions.
how does concentration increase rate of reaction
more collisions per second per unit volume, as there are physically more particles to collide. as reactants get used up, their concentration decreases.
how do catalysts work
increase rate of reaction without themselves being chemically changed. they bring down the activation energy by bringing the reactive parts of the reactant particles into close contact. this provides an alternative pathway for the reaction with lower activation energy.
how can you find rate of reaction from a graph
find the gradient by change in y over change in x
maxwell boltzmann distribution graph axis’
y: number of particles x: kinetic energy
describe increasing temperature and its effect on a maxwell boltzmann graph
the area under the curve does not change as the total number of particles remains constant. more particles have a high velocity, so the curve broadens to the right of the original peak
describe decreasing temperature and its effect on a maxwell boltzmann graph
the area under the curve does not change as the total number of particles remains constant. peaks higher and before the original peak.
describe adding a catalyst and its effect on a maxwell boltzmann graph
no change. mark the lower activation energy on the graph though.
describe changing volume and its effect on a maxwell boltzmann graph
no change
describe adding an inert gas and its effect on a maxwell boltzmann graph
no change