Physical changes and chemical reactions, Gas pressure, The reactivity series, Rusting of iron, Hydrocarbons, Energy changes, Displacement reactions, Extracting metals, Percentage loss or gain

Question 1

Physical changes:

Answer 1

1. Do not make new substances
2. Are often easy to reverse
3. The substances may change state or just be
   mixed together.
4. Examples include: melting, boiling, condensing,
   freezing.

Question 2

Chemical reactions:

Answer 2

1. Always make one or more new substances.
2. Are usually difficult to reverse.
3. The new substances have different properties
   from the original substances.
4. Examples include combustion, neutralization,
   thermal decomposition.

Question 3

Cause of gas pressure:

Answer 3

the force of the particles hitting the walls of the container.

Question 4

What do metals that react with water produce?

Answer 4

metal hydroxide and hydrogen

Question 5

What do metals that react with dilute acids produce?

Answer 5

salt and hydrogen

Question 6

Highest reactive element?

Answer 6

Potassium (K)

Question 7

Lowest reactive element?

Answer 7

Platinum

Question 8

What is steel?

Answer 8

an alloy containing iron mixed with
small amounts of carbon and sometimes
other metals

Question 9

What do iron and steel need or them to rust?

Answer 9

air and water

Question 10

How can rusting be prevented?

Answer 10

1. A physical barrier to stop the air and
   water being in contact with the iron.
2. Sacrificial protection, in which blocks of
   a more reactive metal, such as zinc or
   magnesium, are attached to the iron.
   They then corrode instead of the iron.

Question 11

What do Hydrocarbons contain?

Answer 11

These substances contain hydrogen and carbon only.

Question 12

Carbon dioxide and water:

Answer 12

hydrocarbon + oxygen → carbon dioxide + water

Question 13

Exothermic reactions:

Answer 13

Exothermic reactions transfer energy from the reactants to the surroundings. The temperature
of the surroundings increases.

Question 14

Endothermic reactions:

Answer 14

Endothermic reactions use energy transferred from the surroundings to the reactants. The
temperature of the surroundings decreases.

Question 15

In a displacement reaction…

Answer 15

A more reactive metal takes the place of a less reactive metal in a compound.

Question 16

Most metals occur as…

Answer 16

compounds in ores in the Earth’s crust. Only a few, such as silver and gold, occur as the metallic element.

Question 17

The metals high in the reactivity series are…

Answer 17

difficult to chemically extract from their ores and
their isolation has happened relatively recently.

Question 18

The metals lower in the reactivity series are…

Answer 18

easier to extract from their ores and they have
been available to use as the pure elements for much longer.

Question 19

Metals from zinc downwards in the reactivity series can be…

Answer 19

extracted from their ores by heating
with carbon.

Question 20

Metals above zinc in the reactivity series need…

Answer 20

electrolysis to extract them from their ores.

Question 21

1. Oxidation is the…
2. Reduction is the…

Answer 21

1. gain of oxygen.
2. loss of oxygen.

Question 22

Percentage loss or gain formula:

Answer 22

original amount/actual change × 100