5 Kinetics

Question 1

explain kinetic theory

Answer 1

for a chemical reaction to take place particles need to collide.They need to collide with correct orientation and they need to collide with energy the same or more than the activation energy

Question 2

define activation energy

Answer 2

the minimum energy particles must have upon collision for a successful reaction to take place

Question 3

explain how increasing the temprature increases the rate of reaction

Answer 3

high temperature means particles have more energy increasing the speed of particles and so increasing the frequency of successful collisions

Question 4

explain how increasing the conecntraion of solution increases the rate of reaction

Answer 4

there are more particles in a given volume increasing the frequency of successful collisions

Question 5

explain how pressure increases the rate of a gas reaction

Answer 5

there are more particles in a given volume increasing the frequency of successful collisions

Question 6

explain how surface area of solid reactants increase the rate of reaciton

Answer 6

by breaking solid lumps into smaller particles means more particles are available to collide with molecules in a gas or a liquid increasing the frequency of successful collisions

Question 7

what is the meaning of the term catalyst and how does it work

Answer 7

A catalyst is a substance that increases the rate of a chemical reaction without being changed.It provides an alternative reaction pathway with a lower activation energy

Question 8

what happens in endothermic reaqctions with refrecne to the sourrouindings and what is the sign of ∆H

Answer 8

surroundings gets cooler as heat energy is given in

Question 9

what happens in exothermic reaqctions with refrecne to the sourrouindings ∆H

Answer 9

surroundings gets hotter as heat energy is given out

Question 10

is ∆H negative of positiove for endothermic reactions state why

Answer 10

positive because the products have more energy than the reactants

Question 11

is ∆H negative or positive for exothermic reactions state why

Answer 11

negative because the products have less energy than the reactants

Question 12

deifne rate of reaction

Answer 12

the change in the concentration of product or reactant over time

Question 13

what is the equation used to calculate rate of a reaction

Answer 13

amount of reactant used or product formed/time

Question 14

explain why most collisions do not lead to a reaction.

Answer 14

because most particles collide with energy less than activation energy.Particles need to collide with energy greater or equal to activation energy to react and stick to form a product

Question 15

what is a trasnition state

Answer 15

the species that exists at the top of the curve of an enthalpy diagram

Question 16

what does the Maxwell-Boltzmann distribution tell us about the distribution of energy amongst the particles

Answer 16

no particles have zero energy
most particles have intermediate energies - around the peak
few particles have very high energies -RHS of the curve

Question 17

where is the most probable energy on the M.B.D curve

Answer 17

at the peak

Question 18

where is the average energy on the M.B.D curve

Answer 18

to the left of the peak(most probable energy)

Question 19

what does the x axis on the M.B.D curve represent

Answer 19

energy

Question 20

what does the y axis on the M.B.D curve represent

Answer 20

number of particles

Question 21

what does the area under the M.B.D curve represent

Answer 21

the number of particles

Question 22

explain what happens to the sshape of the curve when temperature increases

Answer 22

the peak of the curve is lower and shifts to the right and the endof the curve is raised higher so more pearticles have energy greater than Ea

Question 23

what is the abbreviation used for activation energy

Answer 23

Ea

Question 24

why is the total area under the graph the same for different temperatures

Answer 24

because are under the graph only represents the total number of particles

Question 25

with reference to the M.B.D explain why an increase in temperature decreases the rate of reaction

Answer 25

more of the particles have energy greater than or equal to Ea so more particles have sufficient energy to react increasing the frequency of successful collisions

Question 26

state why the M.B.D curve starts at the origine

Answer 26

because there are no particles with zero energy

Question 27

with reference to the M.B.D explain why a decrease in temperature decreases the rate of reaction

Answer 27

because fewer particles will have energy more than or equal to activation so less particles have suffieicnet energy to react decreasing the frequency of successful collisons

Question 28

explain why a small increase in temperature has large effect on the initial rate of reaction

Answer 28

a small increase in temperature results in significantly more particles colliding with energy equal to or greater than activation energy

Question 29

with reference to the M.B.D explain how a catalyst increases the rate of a reaction

Answer 29

a catalyst provides an alternative reaction pathway with a lower activation energy and so more particles will have energy equal to or greater than activation energy and more particles will have sufficeint energy to react increasing the frequency of successful collisions and therefore increases the rate of reaction

Question 30

how would the M.B.D curve look when a catalyst is added and state the how it affects the activation energy

Answer 30

Ea on the axis will shift to the left and so more particles will have energy greater or the same as Ea

Question 31

describe how a catalyst affects enthalpy change

Answer 31

they have no effect on the enthalpy change

Question 32

describe how a catalyst affects activation energy

Answer 32

it provides an alternative reaction pathway with a lower the activation energy so more particles will have energy greater or equal to Ea

Question 33

describe how a catalytic coverter looks like

Answer 33

converter is a honeycomb coated with platinum and rhodium metals.These are the catalysts.Has large Surface ara

Question 34

explain how a catalytic convertor work with reference to adsorption and desorption

Answer 34

adsorption: gases form weak bonds with metal atom of surface of the catalyst.The bonds must be strong enough to hold the gases for long enough to react and weak enough to relase the products easily
desporption: products break away from metal atom freeing up more room on the surface of the catalyst for more gases to react

Question 35

what does the area under a particular region of a curve represent

Answer 35

number of particles that can react