Chemical Changes

Question 1

A physical change happens when

Answer 1

No new substances are formed

Question 2

Is there a change in chemical properties during a physical change?

Answer 2

No

Question 3

Can physical changes usually be reversed?

Answer 3

Yes

Question 4

What is a chemical change ?

Answer 4

A change in which new substances (in the form of elements and/or compounds) are formed

Question 5

What are the 4 signs of chemical changes

Answer 5

1. Release or gain of energy
2. Changes in colour and odour
3. Formation of gas or solid
4. Not easily reversible

Question 6

Physical change vs Chemical Change

Answer 6

1. No new substances formed vs new substances formed (products)
2. usually reversible vs usually irreversible
3. No change in chemical properties vs products have different chemical properties than its constituents
4. Constituents can be obtained easily via separation techniques vs cannot be obtained easily

Question 7

What are the 5 types of chemical reactions

Answer 7

1. Combustion
2. Oxidation
3. Thermal decomposition
4. Electrolysis
5. Neutralisation

Question 8

Define combustion

Answer 8

It is a chemical reaction in which a substances reacts with oxygen to form one or more new substances and heat is given off

Question 9

What is the word equation for combustion

Answer 9

Carbon + oxygen -> carbon dioxide

Question 10

What is oxidation

Answer 10

When a substance gains oxygen

Question 11

Give 2 examples of oxidation

Answer 11

Rusting of iron
Cellular respiration

Question 12

What is thermal decomposition

Answer 12

A process in which one substance breaks down into 2/more simpler substances upon heating

Question 13

What is electrolysis

Answer 13

It is a chemical reaction brought about by passing an electric current through and electrolyte

Question 14

What is an electrolyte

Answer 14

It is a liquid which can conduct electricity due to the presence of ions

Question 15

Name 2 functions of electrolysis

Answer 15

1. Cause the decomposition of water to form oxygen and hydrogen
2. Used to coat ab object with metal ( known as electroplating)

Question 16

What is neutralisation

Answer 16

Chemical reaction when an acid is mixed with alkali

Question 17

Name 5 characteristics of acids

Answer 17

1. pH < 7
2. turns damp blue litmus paper red
3. Reacts with alkalis, reactive metals and carbonates
4. Can conduct electricity
5. Taste sour

Question 18

Name 6 characteristics of alkalis

Answer 18

1. pH > 7
2. Turns damp red litmus paper blue
3. Reacts with acids
4. Can conduct electricity
5. Bitter taste
6. Soapy feel