Chemical Reactions

Question 1

How would you classify a reaction as a chemical change and a physical change?

Answer 1

A chemical change is when something new is formed. The original substance changes into another substance that is different.
A physical change is when the substance remains the same. It may look or feel different but there is no chemical change.

Question 2

What are the characteristics of chemical and physical changes?

Answer 2

Physical Changes
- Anything to do with its physical appearance. E.g. brittleness

Chemical Changes
- Anything to do with a chemical reaction.

Question 3

What is the difference between the physical properties and chemical properties of a substance?

Answer 3

Physical properties - characteristics that can be observed all measured without changing the substances chemical identity. Examples include colour, odour, state of matter, solubility, density and hardness

Chemical properties - how are substance interact with other substances; involve a changing chemical identity. Examples include flammability, reactivity with acids and bases, ability to rust (oxidation), combustion and decomposition

Question 4

What is an oxidation reaction?

Answer 4

A reaction where oxygen bonds with a substance.

Question 5

What is a chemical reaction where a substance combines with oxygen rapidly giving out energy?

Answer 5

Combustion reaction

Question 6

Describe the combustion of the element magnesium in oxygen. Include what you would observe and name the product.

Question 7

Describe the combustion of the element magnesium in oxygen. Include what you would observe and name the product. Additionally state the symbol equation.

Answer 7

• chemical exothermic reaction
• producing magnesium oxide
• intense white flame
• white powder produced (magnesium oxide)
• 2Mg (s) + O2 (g) —> 2MgO (s)

Question 8

Describe the combustion of the element sulphur in oxygen. Include what you would observe and name the product. Additionally, state the symbol equation.

Answer 8

• chemical, exothermic reaction
• blue flame
• colourless, poisonous gas produced (sulphur oxide)
• S (s) +O2 (g) —> SO2 (g)

Question 9

Describe the combustion of the element hydrogen in oxygen. Include what you would observe and name the product. Additionally, state the symbol equation.

Answer 9

• chemical, exothermic reaction
• water is produced
• 2H2 (g) + O2 (g) —> 2H2O (g)

Question 10

Are solutions of metal oxides acid or alkaline?

Answer 10

Alkaline

Question 11

Are solutions of non-metal oxides acidic or alkaline?

Answer 11

Acidic

Question 12

What is a fuel?

Answer 12

A substance that when burned in oxygen releases energy.

Question 13

What is a hydrocarbon?

Answer 13

A compound made up of hydrogen and carbon atoms only.

Question 14

What is a word equation for the combustion of hydrocarbons.

Answer 14

Methane + oxygen —> carbon dioxide + water

Question 15

Bob bubbled a gas through limewater and the limewater turned cloudy. What gas was Bob using?

Answer 15

Carbon dioxide

Question 16

What paper turns from blue to pink when mixed with water?

Answer 16

Cobalt chloride paper

Question 17

What does cobalt chloride paper do when water is added to it?

Answer 17

Turns from blue to pink

Question 18

What is the chemical test for water?

Answer 18

Cobalt chloride paper turns from blue to pink

Question 19

Define thermal decomposition.

Answer 19

The breaking down of a substance through heat.

Question 20

Do all carbonates decompose through heating?

Answer 20

No

Question 21

What is the word equation for the thermal decomposition of metal carbonates?

Answer 21

________ carbonate —> _________ oxide + carbon dioxide

Question 22

What is an exothermic reaction?

Answer 22

A reaction in which heat energy is released.

Question 23

What is an endothermic reaction?

Answer 23

A reaction where heat energy is taken in.

Question 24

An acid ranges between which numbers on the pH scale?

Answer 24

1-6

Question 25

Name three examples of acids.

Answer 25

Lemon juice, hydrochloric acid, sulphuric acid

Question 26

An alkali ranges between which numbers on the pH scale?

Answer 26

8-14

Question 27

Name three examples of an alkali.

Answer 27

Sodium hydroxide, ammonia, toothpaste

Question 28

What is a neutral substance?

Answer 28

A substance with a pH level of 7.

Question 29

How do you prepare a salt?

Answer 29

By neutralising an acid and an alkali.

Question 30

Describe a neutralisation reaction.

Answer 30

Where an acid and an alkaline mix and produce water and salt.

Question 31

Give a word equation for a neutralisation reaction.

Answer 31

Copper oxide + sulphuric acid —> copper sulfate + water

Question 32

Give two ways of increasing the speed of a reaction.

Answer 32

Using a catalyst or increasing the temperature.

Question 33

Explain why increasing the temperature increases the speed of a reaction and vice versa.

Answer 33

Because there is more energy, therefore the reactant particles move more quickly, colliding more often increasing the rate of reaction.

Question 34

After a catalyst has been added, the reaction remains chemically ___________.

Answer 34

Unchanged