[C7] Chemical reactions

Question 1

What is the collision theory?

Answer 1

Collision theory states that in order for a reaction to occur:
The particles must collide with each other. The collision must have sufficient energy to cause a reaction i.e. enough energy to break bonds

Question 2

What is activation energy?

Answer 2

The minimum energy that colliding particles must have to react is known as the activation energy

Question 3

What are successful collisions?

Answer 3

Collisions which result in a reaction are known as successful collisions
If they have sufficient energy (i.e. energy greater than the activation energy), they will react, and the collision will be successful

Question 4

How do unsuccessful collisions occur?

Answer 4

Unsuccessful collisions happen when the colliding species do not have enough energy to break the necessary bonds (i.e. they collide with energy less than the activation energy)

Question 5

What is the rate of reaction?

Answer 5

The rate of reaction is a measure of how fast or slow a chemical reaction is.

Question 6

How is it calculated?

Answer 6

It is calculated by how much reactant is used per unit time OR how much product is produced per unit time.

Question 7

How can it be altered/changed?

Answer 7

Changing the conditions a reaction occurs in can alter the rate of the reaction.*

Question 8

What is a physical change?

Answer 8

Physical changes are changes affecting the form of a chemical substance, but not its chemical composition.
eg. melting or evaporating

Question 9

What is a physical change?

Answer 9

Physical changes are changes affecting the form of a chemical substance, but not its chemical composition.
eg. melting or evaporating

Question 10

Are physical changes reversable?

Answer 10

These changes are often easy to reverse

Question 11

What are chemical changes?

Answer 11

Chemical changes (usually referred to as chemical reactions) are reactions where new chemical substances are formed that have very different properties to the reactants.

Question 12

What changes accompany chemical changes?

Answer 12

There may be signs that a new substance has formed, such as:
A colour change
A precipitate being formed
Bubbles of gas being produced

Energy changes also accompany chemical changes and energy can be given out (exothermic) or taken in (endothermic)

Question 13

What is the effect of temperature on the rate of reaction?

Answer 13

Increasing the temperature will increase the rate of reaction

This is because the particles will have more kinetic energy than the required activation energy

Question 14

What is the effect of temperature on collisions?

Answer 14

The effect of temperature on collisions is not so straightforward as concentration or surface area; a small increase in temperature causes a large increase in rate

Question 15

What is the effect of concentration in a reaction?

Answer 15

Increasing the concentration of a solution increases the collision rate.

This is because there will be more reactant particles per unit volume, causing more frequent collisions so there are more successful collisions per second, increasing the rate of reaction.

Question 16

What effect does surface area have on rate of reaction? Why?

Answer 16

Increasing the surface area of a solid will increase the rate of reaction

This is because more surface area of the particles will be exposed to the other reactant, producing a higher number of collisions per second

Question 17

What effect do catalysts have on the rate of reaction?

Answer 17

substances which speed up the rate of a reaction without themselves being altered or consumed in the reaction

Question 18

What are some examples of catalysts?

Answer 18

An important industrial example is iron, which is used to catalyse the Haber Process for the production of ammonia

Iron beads are used to increase the surface area available for catalysis

Question 19

What is a redox reaction?

Answer 19

Oxidation–reduction reactions, commonly known as redox reactions, are reactions that involve the transfer of electrons from one species to another.

Question 20

What is oxidation and reduction?

Answer 20

Oxidation is a reaction in which oxygen is added to an element or a compound

Reduction is a reaction in which oxygen is removed from an element or compound

Question 21

Why is there a risk of explosion in factories that deal with flour?

Answer 21

Flour particles have a large surface area. When there is a lot of flour in the air, a small spark from an operating machine can cause a reaction between the flour and the spark.
This can result in a dangerous explosion.