rate equations

Question 1

definition of rate of reaction

Answer 1

change in concentration per unit time

Question 2

why does higher temp increase rate of reaction

Answer 2

higher temp - many more particles have energy greater than Ea
more frequent succesful collisions

Question 3

why does a higher conc/pressure increase rate of reaction

Answer 3

more particles in a given volume
more frequent successful collisions

Question 4

why does breaking a solid into smaller particles increase the rate

Answer 4

surface area increases
more particles available for collisions
more frequent successful collisions

Question 5

what is a catalyst and how does it work

Answer 5

a substance that increases the rate of reaction without being used up
provides an alternate reaction route with a lower activation energy

Question 6

key points of a maxwell distribution curve

Answer 6

-x axis - kinetic energy
-y axis - number of particles with ke
-curve must start at the origin(0 particles with 0 energy)
-peak of curve - most probable energy
-area under curve - total number of particles
-Ea - activation energy
- asymptote to x axis at the end
- only particles that have ke larger than activation energy have a successful collision

Question 7

maxwell distribution with an increase in temperature

Answer 7

curve shifts to the rhs and lower peak
at higher temp many more particles have energy greater than Ea
more frequent successful collisions

Question 8

maxwell distribution with an decrease in temperature

Answer 8

curve shifts to the left hand side and peak is higher
at lower temp fewer particles have energy greater than Ea
less frequent successful collisions

Question 9

maxwell distribution with an increase in conc or pressure

Answer 9

curve higher original curve
more particles in a given volume
more frequent successful collisions

Question 10

maxwell distribution with a catalyst

Answer 10

same curve
activation energy is lower
more particles have energy greater than Ea
more frequent successful collisions

Question 11

zero order

Answer 11

changing the concentration of a reactant has no effect on the rate of reaction
[x]^0
horizontal graph

Question 12

first order

Answer 12

as the conc increases the rate increases by the same amount
directly proportional
[X]

Question 13

second order

Answer 13

as conc increases rate increases by that amount squared
exponential curve
[X]^2

Question 14

using a large excess of a reactant

Answer 14

will mean that the order of reaction is 0 with respect to that reactant as the reactants concentration is effectively constant

Question 15

rate constant k

Answer 15

only temp changes the value
rate of reaction when all concentrations are 1moldm-3
units always end in s-1

Question 16

continuous monitoring method
CMM

Answer 16

following the course of a single reaction
2 ways to measure the progress of a reaction
1-by taking samples at regular intervals
2-by using a physical indicator such as gas volume

Question 17

problem with CMM
1-taking samples at regular intervals

Answer 17

problem - the reaction mixture is still reacting
to solve the problem - to stop (quench) the reaction add a large volume of cold distilled water
this will both cool and dilute the reaction decreasing the rate

Question 18

problem with CMM
2 - by using a physical indicator

Answer 18

problem - this records the amount of product produced
the order of reaction is about reactants
the volume recorded would need converting to reactant concentration

Question 19

using the results from CMM

Answer 19

plot a concentration time graph
rate of reaction = gradient of the tangent
to work out order - take 2 different tangents at different concentrations and compare the scale factor of concentration and rate of reaction
if the graph is straight - zero order

Question 20

initial rates method

Answer 20

series of experiments where concentration changes in each one with all other factors are constant
time it takes to get to a specific point in reaction is recorded eg colour change

Question 21

IRM
What do u measure for

Answer 21

time recorded when observation occurs
rate = 1/time
concentration does not need to be known as total volume is constant so the volume of reactant is proportional to its concentration.

Question 22

to carry out an iodine clock initial rates practical

Answer 22

-measure out known volumes of reactants
keep them separate so the reaction doesnt start
-start the stopwatch when the last of the reactant is added to a conical flask.
-stop the timer when the observation occurs and record
-repeat the experiment using the same total volume altering the concentration
rate = 1/time
plot a graph of rate by concentration

Question 23

Arrhenius equation

Answer 23

k=Ae^-Ea/RT
k=rate constant
A=Arrhenius constant (same units as k)
e=math constant
Ea=activation energy
r=molar gas constant - 8.31
t=temp in kelvin

gradient of a line = -Ea/R

Question 24

rate determining step

Answer 24

slowest step
RDS contains the same species as the rate equation in the same amounts