Rates of Reaction

Question 1

what is needed for a reaction to occur?

Answer 1

1. particles must collide with sufficient energy which overcomes the activation energy.
2. particles must collide with the correct collision geometry.

Question 2

activation energy definition

Answer 2

the minimum kinetic energy required for a reaction to occur.

Question 3

activated complex definition

Answer 3

an unstable arrangement of atoms. It is an intermediate between reactants and products.

Question 4

what is an enzyme

Answer 4

a biological catalyst

Question 5

homogeneous catalyst

Answer 5

a catalyst in the same physical state as the reactants

Question 6

heterogeneous catalyst

Answer 6

a catalyst in a different physical state from the reactants.

Question 7

how does using a catalyst increase the rate of reaction?

Answer 7

it provides an alternative reaction pathway with a lower activation energy.

Question 8

negative effect if a reaction is too slow

Answer 8

it will not be economically viable

Question 9

negative effect if a reaction is too fast

Answer 9

there will be a risk of explosion

Question 10

average rate of reaction equation

Answer 10

average rate = change in q/change in t

Question 11

relative rate equation

Answer 11

relative rate = 1/t units s^-1

Question 12

do reactants with energy greater than that activation energy always collide?

Answer 12

no, they also need the correct collision geometry.

Question 13

what happens to catalysts at the end of a reaction?

Answer 13

they are regenerated and therefore can be used again.

Question 14

temperature definition

Answer 14

a measure of the average kinetic energy of all the particles in a sample.

Question 15

effect of increasing temperature

Answer 15

the number of particles with Ek above Ea increases

when drawing graph: Ea stays the same, area under graph stays the same so draw to the right and slightly lower down

Question 16

potential energy diagram purpose

Answer 16

shows the progress of a reaction from reactants to products

Question 17

decreasing particle size

Answer 17

decreasing particle size increases surface area of the reactant.
more particles exposed results in greater chance of successful collisions, therefore increased rate of reaction.

Question 18

increasing concentration

Answer 18

increases the number of particles. more particles result in greater chance of successful collisions, therefore increased rate of reaction

Question 19

increasing temperature

Answer 19

increase speed of particles
particles moving at a greater speed result in more successful collisions, therefore increased rate of reaction.
more particles have energy greater than or equal to the activation energy.

Question 20

increasing pressure

Answer 20

reactant particles are pushed closer together (same number of particles in a smaller volume). Therefore, more chance of successful collisions and increased rate of reaction.

Question 21

when is relative rate calculation used

Answer 21

when it is difficult to measure the change in a chemical reaction (colour change etc)

Question 22

enthalpy change equation

Answer 22

Hp-Hr

Question 23

enthalpy change for exothermic reactions

Answer 23

negative

Question 24

enthalpy change for endothermic reactions

Answer 24

positive

Question 25

why a small change in temperature can produce a large change in reaction rate

Answer 25

because increasing the temperature increases the number of successful collisions because there are more molecules with energy greater than the activation energy.

Question 26

how heterogeneous catalysts work

Answer 26

1. adsorption: reacting molecules are adsorbed onto active sites.
2. reaction: reaction occurs on the surface with less energy needed to form activated complex.
3. desorption: product molecules are formed and leave the catalysts surface free for further reactions.

Question 27

catalyst poisoning

Answer 27

heterogeneous catalysts are easily poisoned to the extent that their activity can be greatly reduced or stopped completely
the poison particles form strong bonds with the surface of the catalyst blocking the active sites.

Question 28

examples of catalyst poisoning

Answer 28

if lead poisons a catalytic converter in a car it would be rendered useless.

Question 29

what are energy distribution diagrams also known as?

Answer 29

Maxwell-Boltsman distribution curve

Question 30

what does area under energy distribution diagram equal?

Answer 30

number of molecules in sample

Question 31

general rule of thumb when increasing temperature by 10 degrees

Answer 31

rate of reaction doubles

Question 32

enzyme optimum temperature

Answer 32

enzyme activity increases until it reaches a peak

this is the temp at which enzyme works best

Question 33

what happens to enzyme after optimum temperature

Answer 33

rate will fall drastically to zero

hydrogen bonds break and protein unravels and changes shape (denaturing)

Question 34

denatured enzyme

Answer 34

enzymes no longer work and so their activity (rate) falls to zero.

Question 35

examples of enzymes in nature

Answer 35

-catalase: breaks down hydrogen peroxide

Question 36

examples of enzymes in industry

Answer 36

-zymase: converts glucose into alcohol in the brewing industry