3.1.5 Kinetics

when will an ineffective / inelastic collision occur

when particles don't have enough energy for a reaction/ wrong alignment or orientation

activation energy

the minimum energy required for particles to collide to start a reaction

why should the energy distribution of a Maxwell Boltzmann distribution go through the origin

there are no molecules with no energy

whats the Emp of the Maxwell Boltzmann distribution

most probably energy

the peak of the curve

where is the mean usually on the Maxwell Boltzmann distribution

to the right of the Emp

what does the area under the curve of the Maxwell Boltzmann distribution represent?

total number of particles present

why should the curve of the Maxwell Boltzmann distribution never meet the x axis

there is no maximum energy for molecules

x axis of the Maxwell Boltzmann distribution

energy

y axis of the Maxwell Boltzmann distribution

number of molecules

how can a reaction go to completion if few particles have energy greater than Ea?

Particles can gain energy through collisions

as temperature increases, what happens to the Maxwell Boltzmann distribution

it shifts down and right

why does the M-B curve shift down and right when the temp is increased?

more molecules with higher energies (both the Emp and mean energy shift to higher energy values but the number of molecules with those energies decrease because the molecules have a wider range of energies)

Why should the total area under the curve remain constant when the temperature is increased?

bc the total number of particles is constant

rate of reaction

The change in concentration of a substance over time

usual unit of rate of reaction

mol dm-3 s-1

whats the gradient of the curve when a graph of concentration of reactant is plotted vs time

rate of reaction

initial rate

rate at the start of the reaction where it is fastest

how to measure rate of reaction in experiment between sodium thiosulfate and hydrochloric acid

1/time

why can we use 1/time to measure the rate of reaction in the experiment between sodium thiosulfate and hydrochloric acid

bc we can assume the amount o sulfur produced is fixed and constant

concentration

measure of the number of particles per unit volume

effect of increasing concentration/ pressure on rate of reaction

more particles per unit volume

so more particle collisions

so more effective collisions

=faster rate of reaction

If a question mentions doubling of concentration/ rate, what should you mention

double the number of particles per unit volume

double the frequency of effective collisions

effect on M-B curve when concentration/ pressure is increased

shape of curve stays the same

curve will be higher (bc more particles per unit volume)

Comparing rate curves

catalyst definition

increase rates of reaction without getting used up

catalysts explanation

they provide an alternative route or mechanism with a lower activation energy

effect of catalyst on M-B curve

Ea lowers (so more particles have the activation energy, so higher frequency of effective collisions)

how does the enthalpy change for a catalysed reaction change?

it doesn't