Topic 7: Rates of Reaction and Energy Changes

Question 1

What does rate of reaction mean?

Answer 1

How quickly a reaction happens

Question 2

What are the 2 ways that rate of reaction can be calculated?

Answer 2

1. rate of reaction = amount of product formed/time
   OR
2. rate of reaction = amount of reactant used/time

Question 3

What are the common units of rate of reaction?

Answer 3

g/s
cm3/s
mol dm3/s

Question 4

What are the 3 ways to measure rate of reaction?

Answer 4

1. Time it takes for the reactants to form a precipitate
2. The change in mass over time (mass after reaction - mass before reaction)
3. Volume of gas produced over time

Question 5

What goes on the x axis and on the y axis of a rate of reaction graph?

Answer 5

Y axis - amount of product formed
X axis - time

Question 6

What does a steep line show on a rate of reaction graph?

Answer 6

A faster rate of reaction

(The steep the line, the faster the rate of reaction)

Question 7

What do flat lines show on a rate of reaction graph?

Answer 7

The reaction has finished

Question 8

If more reactant is used in a reaction, how does it affect how much product is formed?

Answer 8

The more reactants used, the more products formed

Question 9

How can you find the rate of reaction on a rate of reaction graph?

Answer 9

The gradient

Question 10

How to calculate gradient?

Answer 10

Gradient = change in y/change in x
OR
Gradient = rise/run

Question 11

What’s the process to find the rate of reaction at a specific point (if it’s on a curve) on a rate of reaction graph?

Answer 11

1. Draw a tangent to the curve at that point
2. Then create triangle in dotted lines - to find the gradient

Question 12

What are the 4 factors affecting rates of reaction?

Answer 12

1. Temperature
2. Pressure or concentration
3. Surface area
4. Catalysts

Question 13

What is activation energy?

Answer 13

The minimum amount of energy that particles need to react

Question 14

What 2 things does rate depend on with collision theory?

Answer 14

Collision frequency - the more collisions between particles, the faster the rate of reaction
&
Collision energy - the more collisions with at least the activation energy, the faster the rate of reaction

Question 15

If there is high energy and high frequency when particles collide, what happens to the rate of reaction?

Answer 15

The rate of reaction is fast

Question 16

If there is low energy and low frequency when particles collide, what happens to the rate of reaction?

Answer 16

The rate of reaction is slow

Question 17

If a reaction is done at a high temperature, what happens to the rate of reaction? Why?

Answer 17

The rate of reaction is fast - particles move faster - collide more frequently with more heat energy

Question 18

If the reaction is done at a cold temperature, what happens to the rate of reaction? Why?

Answer 18

The rate of reaction is slow - particles move slower - collide less frequently with less heat energy

Question 19

If the reaction is done at a high pressure or concentration, what happens to the rate of reaction? Why?

Answer 19

The rate of reaction is fast - the more particles in the same volume, the more frequent the collisions

Question 20

If the reaction is done at a low pressure or concentration, what happens to the rate of reaction? Why?

Answer 20

The rate of reaction is slow - the less particles in the same volume, the less frequent the collisions

Question 21

If the reaction has particles with a small surface area in the reaction, what happens to the rate of reaction? Why?

Answer 21

The rate of reaction is fast - more area for particles to collide with - more frequent collisions

Question 22

If the reaction has particles with a large surface area in the reaction, what happens to the rate of reaction? Why?

Answer 22

The rate of reaction is slow - less area for particles to collide with - less frequent collisions

Question 23

As size of particles in a reaction decreases, what happens to the surface area to volume ratio?

Answer 23

The surface area to volume ratio is larger - less surface area of particles within a large volume

Question 24

What is a catalyst?

Answer 24

Speeds up a reaction without being chemically changed or used up in the reaction, and without changing the products

Question 25

What happens to activation energy when a catalyst is used in a reaction? Why?

Answer 25

It’s lower - allows more collisions to have energy to react with each other - increases rate of reaction

Question 26

What is an example of a catalyst? What’s a use for it?

Answer 26

An enzyme - used to make alcoholic drinks

Question 27

What 2 types of energy transfers are there?

Answer 27

1. Endothermic reaction 2. Exothermic reaction

Question 28

What is an endothermic reaction?

Answer 28

A reaction that takes in heat energy from the surroundings

Question 29

What is an endothermic reaction shown by?

Answer 29

A decrease in temperature

Question 30

What is an exothermic reaction?

Answer 30

A reaction that gives out heat energy to the surroundings

Question 31

What is an exothermic reaction shown by?

Answer 31

An increase in temperature

Question 32

What equipment is used during the measuring of a temperature change?

Answer 32

1. A thermometer - to measure the temperature 2. Large beaker with a polystyrene cup (with reaction mixture in it and a lid on it) in it 3. Cotton wool around the polystyrene cup - to insulate it

Question 33

How can temperature change be measured?

Answer 33

1. Record initial temperature 2. Record maximum temperature reached 3. Then do: maximum temperature reached - initial temperature

Question 34

What 2 things can the polystyrene cup method, that measures temperature change, be used for?

Answer 34

1. Dissolving salts in water 2. Neutralisation, displacement and precipitation reactions

Question 35

What does the reaction profile of an endothermic reaction look like (talk about: activation energy, energy of reactants and energy of products)?

Answer 35

Activation energy: high Energy of reactants: low Energy of products: high

Question 36

If a reaction profile shows a reaction where the PRODUCTS HAVE MORE energy than the reactants, what type of reaction is it? Has energy been absorbed or released?

Answer 36

Endothermic reaction - energy has been absorbed

Question 37

What does the reaction profile of an exothermic reaction look like (talk about: activation energy, energy of reactants and energy of products)?

Answer 37

Activation energy: low Energy of reactants: high Energy of products: low

Question 38

If a reaction profile shows a reaction where the REACTANTS HAVE MORE energy than the products, what type of reaction is it? Has energy been absorbed or released?

Answer 38

Exothermic reaction - energy has been released

Question 39

Do endothermic reactions break or form bonds?

Answer 39

They break bonds

Question 40

Do exothermic reactions break or form bonds?

Answer 40

They form bonds

Question 41

What is an example of an endothermic reaction?

Answer 41

Photosynthesis

Question 42

Why do endothermic reactions break bonds?

Answer 42

Because energy used to break bonds is greater than energy released by forming new bonds in endothermic reactions

Question 43

Why do exothermic reactions form bonds?

Answer 43

Because energy released by forming bonds is greater than energy used to break existing bonds in exothermic reactions

Question 44

How can overall energy change be calculated?

Answer 44

Overall energy change = total energy needed to break bonds - total energy released by forming bonds