Topic 7- Rates of reaction and energy changes (with spec) paper 2

Question 1

How could you describe the rate of a reaction?

Answer 1

The rate of formation of a product or the rate of removal of a reactant.

Question 2

What is the formula for rate of reaction?

Answer 2

amount of reactant used or amount of product formed ÷ time

Question 3

What are three ways you can measure the rate of a reaction?

Answer 3

Precipitation (mixing two solutions and putting it on a cross), change in mass or volume of gas given off

Question 4

What does having finer particles mean for the rate of the reaction?

Answer 4

It means that it has a larger surface area so it’ll be quicker.

Question 5

What needs to happen for a reaction to take place?

Answer 5

The particles need to collide. They need to collide with enough energy to react. The activation energy is the minimum energy needed.

Question 6

How does concentration affect rate of reaction?

Answer 6

If a solution is more concentrated it increases the rate because more particles are reactant in the same volume. This makes collisions more likely.

Question 7

What factors do reactions depend on?

Answer 7

Temperature, concentration and the size of the particles

Question 8

What does the rate of reaction depend on?

Answer 8

How often particles collide and the energy transferred during a collision.

Question 9

How does temperature affect rate of reaction?

Answer 9

• particles move faster so will have more collisions

- the particles will gain energy meaning there will be more successful collisions

Question 10

How does having a large surface area affect rate of reaction?

Answer 10

• particles will have more area to work on sos the frequency of collisions will increase
• rate is faster for solids with a larger surface area to volume ratio

Question 11

What is a catalyst?

Answer 11

A substance that increases the rate of a reaction without being chemically changed or used up in the reaction.

Question 12

What are three advantages of using catalysts?

Answer 12

• speeds up the reaction
• reduces energy use
• use more than once

Question 13

How do catalysts work?

Answer 13

Decreasing the activation energy needed for the reaction to take place. They provide an alternative reaction pathway that has a lower activation energy.

Question 14

What is activation energy?

Answer 14

the minimum energy needed to start a reaction.

Question 15

What are enzymes?

Answer 15

Biological catalysts that speed up chemical reactions in living cells. They are used to catalyse reactions like respiration and photosynthesis.

Question 16

What is an exothermic reaction?

Answer 16

One which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature.

Question 17

What is an endothermic reaction?

Answer 17

One which takes in energy from the surroundings usually in the form of heat and usually shown by a fall in temperature of the surroundings.

Question 18

What are reaction profiles?

Answer 18

They show the chemical changes (exothermic or endothermic) without a catalyst.

Question 19

Explain the marble chip and hydrochloric acid reaction.

Answer 19

Mix hydrochloric acid with marble chips (small, medium or large) and measure how much gas is in the measuring cylinder until the reaction stops. Repeat the experiment with different size chips at the same mass. The smaller chips release gas the quickest due to a larger surface area so more collisions.

Question 20

What does a graph look like for a endothermic reaction?

Answer 20

Starts low energy and goes up and then stable

Question 21

What does a graph look like for a exothermic reaction?

Answer 21

Starts high energy, goes up slightly and then down then stable

Question 22

Explain the hydrochloric acid and sodium thiosulphate reaction

Answer 22

Measure the hydrochloric acid and sodium thiosulphate and heat it to the desirable temperature separately. Then place the conical flask mixture on top of a cross and put the stopwatch on and measure the time until you can no longer see the cross. The experiment is then repeated with the different temperatures.

Question 23

When is bond breaking and bond forming?

Answer 23

Bond breaking is endothermic

Bond forming is exothermic

Question 24

How do you calculate the overall energy change for a reaction?

Answer 24

overall energy change = energy required to break bonds - energy released by forming bonds
a positive energy change is an endothermic reaction and a negative energy change is an exothermic reaction.

Question 25

What do graphs of concentration look like against time?

Answer 25

He higher the concentration, the higher up the line goes and then levels off

Question 26

What do graphs of mass against time look like?

Answer 26

The higher the mass, the higher the line goes up (the greater volume of gas produced)

Question 27

What do graphs of volume look like against volume?

Answer 27

The greater the bioluminescent (the smaller the particles) the higher the line goes up

Question 28

What are the four ways of measuring temperature change?

Answer 28

• salts dissolving in water
• neutralisation reactions
• displacement reactions
• precipitation reactions

Question 29

Explain the dissolving of salts in water to measure temperature change?

Answer 29

Adding the salt a polystyrene cup of water and measuring the change in temperature when the salt has dissolved. Dissolving ammonium chloride decrease the temp so is endothermic. Dissolving calcium chloride cause temp to rise so is exothermic.

Question 30

Explain the use of neutralisation reactions to see the change in temperature

Answer 30

Reacting an acid and a base to form a salt and water. Most neutralisation reactions are exothermic however the neutralisation reaction of ethanoic acid and sodium carbonate is endothermic.

Question 31

Explain the use of displacement reactions to see the change in temperature in a reaction?

Answer 31

This is when a more reactive element displaces a less reactive element in a compound. These are normally accompanied by a release of energy so they’re exothermic.

Question 32

Explain the use of precipitation reactions to see the change in temperature in a reaction?

Answer 32

Precipitates are insoluble solids which form when two solutions are mixed together. They are exothermic and result in an increase in temperature of the surroundings.

Question 33

How do you calculate the overall energy change?

Answer 33

Energy required to break bonds - energy released by forming bonds

Question 34

What determines whether the overall heat energy change is exothermic or endothermic?

Answer 34

Exothermic- more heat energy is released in forming bonds than is required in breaking bonds

Endothermic- less heat energy is released in forming bonds than is required in breaking bonds