Topic 7 - rates of reaction and energy changes

Question 1

What is the equation for rate of reaction?

Answer 1

Amount of reactant used or product formed/ time

Question 2

What units could be used for rate of reaction?

Answer 2

G/s
Cm^3/s
Mol/s

Question 3

How can you measure the rate of reaction when a gas is given off?

Answer 3

Measure time and collect gas in an upside down measuring cylinder in a trough of water or in a gas syringe to measure the volume of gas produced
Measure time and change in mass

Question 4

How can you measure the rate of reaction when a precipitate is formed?

Answer 4

Put a black cross below a beaker containing one reactant. Time how long it takes for the cross to disappear after the second reactant is added

Question 5

Why is using the precipitation method to investigate rate of a reaction not very accurate?

Answer 5

It’s subjective so people are likely to disagree over the exact point at which the cross is no longer visible

Question 6

How can you measure rate of reaction using a digital balance?

Answer 6

When a gas is produced as this will cause mass to decrease. The experiment can be carried out on a digital balance and the rate of reaction can be calculated by recording the mass at regular time intervals

Question 7

What does ‘activation energy’ mean?

Answer 7

The minimum amount of energy required for a reaction to occur between two reacting particles

Question 8

What must happen for a reaction to occur?

Answer 8

Particles must collide at the correct orientation with sufficient energy to react

Question 9

In terms of particles, what 2 things could happen when the rate of reaction increases?

Answer 9

More frequent collisions

Energy of collisions increases

Question 10

How can the rate of a reaction be increased?

Answer 10

Increase the temperature 
Increase the concentration
Increase the surface area to volume ratio
Add a catalyst 
Increase the pressure (for gases)

Question 11

How does temperature affect the rate of reaction?

Answer 11

It increases it because the reactants have more energy so more particles have activation energy meaning more successful collisions

Question 12

How does surface area affect the rate of reaction?

Answer 12

It increases because a greater surface area means there are more exposed particles so more frequent successful collisions

Question 13

How does a catalyst affect the rate of reaction?

Answer 13

Increases because it provides an alternate reaction pathway with lower activation energy. More particles will have sufficient energy and react so more successful collisions occur in the same time.

Question 14

How does concentration affect the rate of reaction?

Answer 14

Increasing concentration increases the rate of reaction. This is because there are more reacting particles in the same volume so there are more frequent successful collisions.

Question 15

How does pressure affect the rate of a gaseous reaction?

Answer 15

Increases e are more reacting particles in the same volume of gas so more frequent successful collisions occur

Question 16

Marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could you measure the rate of reaction?

Answer 16

Since gaseous carbon dioxide is released, the rate can be measured by using a digital balance to measure the change in mass over a period of time.

Question 17

Marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide, how could the rate of this reaction be increased?

Answer 17

Increase the surface area of the marble chips by turning them into a powder
Increase concentration of acid
Increase temperature

Question 18

After completing an experiment, how can you find the rate of reaction using a graph?

Answer 18

X axis: time
Y:axis amount of reactant used or product formed
Draw a tangent to a point on the graph and find the gradient of this line to find the rate of reaction at that time

Question 19

A graph showing time and the amount of gas given off during an experiment has a steep gradient. What does this tell you about the rate of the reaction?

Answer 19

Fast rate of reaction

Question 20

What is a catalyst?

Answer 20

A substance which speeds up the rate of a reaction without being chemically changed at the end

Question 21

How does a catalyst speed up the rate of a reaction?

Answer 21

It provides an alternate reaction pathway with a lower activation energy

Question 22

What are enzymes?

Answer 22

Enzymes act as biological catalysts that increase the rate of reactions in living cells

Question 23

Which enzyme is used to produce ethanol from glucose?

Answer 23

Yeast

Question 24

What does exothermic mean?

Answer 24

A reaction that gives out energy to the surroundings

Question 25

What does endothermic mean?

Answer 25

A reaction that takes in heat energy from the surroundings

Question 26

Are neutralisation reactions endothermic or exothermic?

Answer 26

Exothermic

Question 27

Are displacement reactions endothermic or exothermic?

Answer 27

Either exothermic or endothermic

Question 28

Is a salt dissolving in water endothermic or exothermic?

Answer 28

Either exothermic or endothermic

Question 29

Are precipitation reactions endothermic or exothermic?

Answer 29

Exothermic

Question 30

How could you measure the temperature change of a neutralisation reaction?

Answer 30

Measure initial temperature of the solutions
Mix both reactants in a polystyrene cup
Record the highest temperature reached
Calculate the temperature change

Question 31

When measure it the temperature change of a reaction, heat loss means that measurements may be inaccurate. How could heat loss be minimised during an experiment?

Answer 31

Use polystyrene cup
Place reaction cup in a beaker full with cotton wool for extra insulation
Lid on the reaction cup

Question 32

In terms of bond energies, what happens during a chemical reaction? Describe exothermic and endothermic reaction in terms of bonds breaking/forming

Answer 32

Energy is needed to break bonds and is released when bonds are made
Exothermic: energy released from breaking bonds is greater than the energy used to make bonds
Endothermic: energy released in forming new bond is greater than the energy used to break only bonds

Question 33

What two types of reaction are exothermic?

Answer 33

Combustion

Neutralisation

Question 34

How can the energy change of a reaction be calculated from bond energies?

Answer 34

Total energy of bonds broken - total energy of bonds made

Question 35

If the energy change of a reaction is negative, is the reaction exothermic or endothermic?

Answer 35

Exothermic, energy has been lost to the surroundings

Question 36

What is a reaction profile p?

Answer 36

A graph showing the relative energies of reactants and products, as well as the activation energy of a reaction