Reaction rates

Question 1

Importance of controlling a chemical reaction

Answer 1

If a reaction is too slow then it is not economically profitable, if the reaction is too fast there is a risk of explosion.

Question 2

Conditions necessary for a chemical reaction to take place

Answer 2

Collisions between reactant particles occur.
Sufficient collision energy to reach or surpass the activation energy
Good collision geometry

Question 3

Factors affecting the rate of reaction

Answer 3

Concentration
Temperature
Particle size
Catalyst

Question 4

Difference between particle size and surface area

Answer 4

Particle size is where the reactants are broken apart into smaller pieces. Surface area is the area on the surface of the reactant.
Increase in surface area means a decrease in particle size
Vice versa.

Question 5

Relative rate of reaction formula

Answer 5

RR = 1/t

Question 6

Temperature explain on relative rate

Answer 6

As the temperature increases the average kinetic energy increases, meaning collisions occur with more energy, meaning there is a larger number of particles equalling or surpassing the activation energy and the reactant particles collide faster, increasing the frequency of collisions. Therefore the rate of reaction increases

Question 7

Amount of temperature increase to double a rate of reaction

Answer 7

10 degrees Celsius

Question 8

Particle size rate of reaction explain

Answer 8

As the particle size decreases the surface area increases, meaning there is more area for reactant particles to collide, meaning that reactant particles collide more frequently, therefore increasing the rate of reaction

Question 9

Concentration explain rate of reaction

Answer 9

As the concentration increases the number of reactant particles increases, meaning that the reactant particles collide more frequently. Therefore the rate of reaction increases.

Question 10

Catalyst explain on the rate of reaction

Answer 10

A catalyst provides an alternative energy pathway, with a lower activation energy.

Question 11

Activated complex definition

Answer 11

The unstable arrangement of atoms formed at the maximum of the potential energy barrier.

Question 12

What happens at an Activated complex

Answer 12

The intramolecular bonds between reactant atoms begin to break down and new intramolecular bonds begin to form to produce products.

Question 13

Activation energy definition

Answer 13

The minimum energy required by colliding particles to form an activated complex.

Question 14

Potential energy diagram

Answer 14

A graph which shows the potential energy of the reactant particles, activated complex and product particles.

Question 15

Potential energy diagram axis

Answer 15

X axis is reaction pathway
Y axis is potential energy (kJmol-1)

Question 16

Activation energy symbol

Answer 16

Ea

Question 17

How do you calculate the activation energy

Answer 17

Difference between reactants and activated complex/
Difference between the products and activated complex

Question 18

Enthalpy definition

Answer 18

The is the measure of chemical energy stored in substances,

Question 19

Collision geometry importance

Answer 19

Particles must collide with correct collision geometry to form an activated complex.

Question 20

Where is the activated complex found on a potential energy diagram.

Answer 20

At the top of the curve.

Question 21

Catalyst effect on the activation energy

Answer 21

The catalyst decreases the activation energy.

Question 22

Calculating enthalpy formula

Answer 22

Delta H = EH(products) - EH(reactants)
(Products minus reactants)

Question 23

How do you know if a reaction is exothermic on a potential energy diagram

Answer 23

The enthalpy is negative

Question 24

How do you know if a reaction is

Question 25

How do you know if a reaction is endothermic

Answer 25

The enthalpy is positive

Question 26

Endothermic reaction definition

Answer 26

A reaction where the product molecules contain more potential energy than the reactants, meaning heat energy is absorbed.

Question 27

Exothermic reaction definition

Answer 27

A chemical reaction where the product molecules contain less potential energy than the reactant molecules, meaning the reaction gives out heat energy.

Question 28

Energy distribution diagram

Answer 28

The graph which shows the number of particles and the energy of the particles.

Question 29

Energy distribution diagram axis

Answer 29

X - kinetic energy
Y- number of particles /collisions

Question 30

Temperature effect on an energy distribution diagram

Answer 30

Increases the width of the graph by increasing the kinetic energy
Decreases the number of collisions/particles slightly due to increase in kinetic energy.
The hump gets wider and shorter.

Question 31

Catalyst effect on an energy distribution diagram

Answer 31

Moves the activation energy left, so more particles are reaching the activation energy.

Question 32

Temperature definition

Answer 32

The average kinetic energy of particles in a substance.

Question 33

Constants in reaction rates experiments

Answer 33

Concentration
Temperature
Volume/ pressure
Particle size

Question 34

Concentration experiment

Answer 34

Sodium thiosulphate plus hydrochloric acid, measure the rate of reaction and repeat with more water diluted in each time. The reaction goes cloudy so put a cross down below the beaker.

Question 35

Temperature experiment

Answer 35

Potassium permanganate + sulphuric acid, the mixture goes from purple to colourless, should record rate of reaction and then repeat with higher temperature.