C3 - Chemical Reactions

Question 1

What is the conservation of mass?

Answer 1

During a chemical reaction, no atoms are destroyed and no atoms are created.

Question 2

What is Avogadro’s constant?

Answer 2

The number of atoms or molecules in one mole of a substance, equal to 6.022 x 10 ²³.

Question 3

What is a limiting reactant?

Answer 3

The reactant that is completely used up in a reaction.

Question 4

The formula which links mass, molar mass and moles?

Answer 4

Mass = moles x Mr

Question 5

Define an exothermic reaction

Answer 5

An exothermic reaction is one which gives out energy to the surroundings, usually in the form of heat, and usually shown by a rise in temperature of the surroundings.

Question 6

Define an endothermic reaction

Answer 6

An endothermic reaction is 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 7

Define an exothermic reaction in terms of bonds

Answer 7

More energy is released in making bonds than is taken in when breaking bonds

Question 8

Define an endothermic reaction in terms of bonds

Answer 8

More energy is taken in to break bonds than is released to make bonds

Question 9

Define activation energy

Answer 9

The minimum amount of energy needed for bonds to break and a reaction to start

Question 10

What is an oxidation reaction?

Answer 10

A loss of electrons in a reaction is called oxidation

Question 11

What is a reduction reaction?

Answer 11

A gain of electrons in a reaction is called reduction

Question 12

Describe a neutralisation reaction

Answer 12

The reaction between acids and bases is called neutralisation.

It produces a salt and water.

When an acid neutralises a base, or vice versa, the products are neutral

Question 13

Fill in the gaps:

Acid + Metal –> ……….. + ………..

Answer 13

Acid + Metal –> Salt + Hydrogen

Question 14

Fill in the gaps:

Acid + Metal Carbnonate –> …….. + …….. + …………

Answer 14

Acid + Metal Carbonate –> Salt + Water + Carbon Dioxide

Question 15

Fill in the gaps:

Acid + Alkali –> …… + ……..

Answer 15

Acid + Alkali –> Salt + Water

Question 16

Explain the term dilute acid

Answer 16

An acid with a low proportion of acid molecules in a set volume of water

Question 17

Explain the term concentrated acid

Answer 17

An acid with a high proportion of acid molecules in a set volume of water

Question 18

Explain the term strong acid

Answer 18

Strong acids ionise almost completely in water.

A large proportion of acid molecules dissociate to release H⁺ Ions

Question 19

Explain the term weak acid

Answer 19

Weak acids do not fully ionise in water.

Only a small proportion of acid molecules dissociate to release H⁺ Ions

Question 20

How does concentration affect pH?

Answer 20

If the concentration of H⁺ increases by a factor of 10, the pH decreases by 1.

Question 21

What is formed at the cathode?

Answer 21

Metals

Question 22

What is formed at the anode?

Answer 22

Non-metals

Question 23

What happens at the cathode during the electrolysis of aqueous solutions?

Answer 23

At the cathode, if hydrogen ions and metal ions are present, hydrogen gas will be produced if the metal is more reactive than hydrogen (e.g. sodium).

If the metal is less reactive than hydrogen (e.g. copper or silver), then a solid layer of the pure metal will be produced instead.

Question 24

What happens at the anode during the electrolysis of aqueous solutions?

Answer 24

At the anode, if halide ions (Cl^-, Br^-, I^-) are present, molecules of chlorine, bromine and iodine will be formed.

If no halide ions are present, then oxygen will be formed from the hydroxide ions.