Topic 6: Chemical reactions

Question 2

What are physical changes?

Answer 2

Changes that involve the states of matter and energy.
They are reversible; there are no new substances made, it is only the appearance of the substance that changes

Question 3

Give examples of physical changes.

Answer 3

Changes in state
Dissolving
Mixing two solids (e.g. sand and soil)

Question 4

What are chemical changes?

Answer 4

Changes that involve the bonds being broken and new ones being formed.
They are often irreversible

Question 5

Give examples of indications of a chemical change.

Answer 5

Bubbles or releasing gas
Absorbing or releasing heat
Changing colour
Releasing an odour
Inability to reverse the change
Precipitation of a solid from a liquid solution
The formation of a new chemical

Question 6

Give examples of chemical changes

Answer 6

Rusting
Neutralisation
Electrolysis
Digestion
Respiration
Souring of milk
Baking a cake

Question 7

What is a reaction rate?

Answer 7

A measure of how long it takes for a reactant to be used up or a product to be formed.

Question 8

What is the rate of reaction affected by?

Answer 8

Temperature
Concentration
Pressure of gases
Surface area of reacting solids
Use of catalysts

Question 9

How does surface area affect reaction rate?

Answer 9

If reactant molecules exist in different phases, the rate of reaction will be limited by the surface area of the phases that are in contact.

Powders react faster than blocks - greater surface area and since the reaction occurs at the surface we get a faster rate

Question 10

How does concentration affect reaction rate?

Answer 10

Increasing the concentration of one or more reactants will often increase the rate of reaction.

Question 11

How does temperature affect reaction rate?

Answer 11

Rate of reactions speed up with increasing temperature

Question 12

How does a catalyst affect reaction rate?

Answer 12

The presence of a catalyst increases the rate of reaction by providing an alternate pathway which has lower activation energy

Question 13

How does pressure affect reactant rates?

Answer 13

Pressure increases the concentration of gases which in turn results in the increase of the rate of reaction.
The reaction rate increases in the direction of less gaseous molecules and decreases in the reverse direction.

Question 14

What does the rate of reaction depend on?

Answer 14

The rate of successful collisions between reactant particles. The more successful collisions there are, the faster the rate of reaction.

Question 15

Explain how surface area affects the rate of reaction (collision theory)

Answer 15

Increase in surface area of a solid reactant results in an increase in the number of collisions and this results in an increase in the number of successful collisions

Question 16

Explain how concentration affects the rate of reaction (collision theory)

Answer 16

More particles in a more concentrated solution so collision rate between reactant particles is higher. The more often the particles collide, the greater the chance they have to overcome the activation energy and of a successful collision occurring.

Question 17

Explain how temperature affects the rate of reaction (collision theory)

Answer 17

As the temperature increases, the reactant particles increase their kinetic energy and they move faster, resulting in more collisions between the particles. Theis causes the reaction rate to increase.

Question 18

Explain how a catalyst affects the rate of reaction (collision theory)

Answer 18

Provides an alternative reaction path which has a lower activation energy. This causes more of the collisions to become successful, increasing the rate of reaction.

Question 19

Explain how pressure affects the rate of reaction (collision theory)

Answer 19

Increase in pressure results in the gas particles being push closer together, increasing the number of particles per unit volume. This means that they collide more frequently, and so the rate of reaction increases.

Question 20

What is a catalyst?

Answer 20

A substance which can alter the rate of a reaction without being chemically change etself

Question 21

Why is a catalyst specific to a particular reaction?

Answer 21

Because different catalysts catalyse different reactions and not all reactions have suitable catalysts.

Question 22

How do you measure rate of reaction?

Answer 22

Measure the rate at which a reactant is used up
Measure the rate at which a product is formed

Question 23

How can the rate of reaction be calculated?

Answer 23

Question 24

Tell me the conditions of a reversible reaction.

Answer 24

1. They eventually reach an equilibrium
2. When the rate of the forward and reverse reactions are equal = equilibrium
3. When the concentrations of the reactants and products remain constant = equilibrium

Question 25

List the factors that affect the position of equilibrium.

Answer 25

Increasing temperature: results in a lower yield of product.
Increasing pressure
Increasing concentration
Using a catalyst: does not affect position of equilibrium but does increase the rate at which equilibrium is reached.

Question 26

What is the haber process?

Answer 26

A major process used for making ammonia

Question 27

Tell me the uses of ammonia.

Answer 27

manufacture of explosives
nitric acid
fertilisers

Question 28

How is ammonia produced?

Answer 28

Question 29

Tell me the conditions of the Haber process.

Answer 29

20000kPa
iron catalyst
450 degrees celsius

Question 30

Why are industrial conditions employed?

Answer 30

To ensure sufficient ammonia is produced at a fast enough rate

Question 31

Tell me the reactions involved in the contact process.

Answer 31

S(s) + O2(g) —> SO2(g)
2SO2(g) + O2(g) ⇌ 2SO3(g)
SO3(g) + H2O(l) —-> H2SO4(l)

Question 32

Tell me the conditions of the contact process.

Answer 32

450 degrees Celsius
Vanadium oxide catalyst
200 kPa

Question 33

What is reduction?

Answer 33

The loss of oxygen from a substance in a reaction
Gain of electrons.
Reduction in oxidation number

Question 34

What is oxidation?

Answer 34

Gain of oxygen
Loss of electrons
Increase in oxidation number

Question 34

What is an oxidising agent?

Answer 34

The substance that brings about oxidation and is reduced itself in the process

Question 35

What is the reducing agent?

Answer 35

A substance that brings about reduction and is itself oxidised during the process.

Question 36

What are spectator ions?

Answer 36

Ions that have not taken part in the reaction