Chap 5 : Chemical Changes

Question 1

What are changes?

Answer 1

Changes are a result of interactions between matter and energy

Question 2

How are changes classified?

Answer 2

Changes can be classified as chemical changes or physical changes.

Question 3

What are examples of physical changes?

Answer 3

Dissolving sugar or salt in
water and evaporation are
examples of physical changes.

Question 4

Are physical changes reversable?

Answer 4

Physical changes are
reversible and do not involve
the formation of new
substances.

Question 5

Are chemical changes irreversable?

Answer 5

Chemical changes are irreversible and involve the
formation of new substances.

Energy in the form of heat, light or electricity may
be taken in or given out during a chemical change.

Question 6

Is rusting a physical or chemical change?

Answer 6

Iron reacts with oxygen and
water in the air to form rust.

Rust is a brown substance.

Hence, rusting is a
chemical change.

Question 7

What are some examples of chemical changes?

Answer 7

rusting,

burning of paper,

photosynthesis

souring of milk

Question 8

What are chemical changes also known for?

Answer 8

Chemical changes are also known as chemical

reactions.

Question 9

When do chemical changes occur?

Answer 9

Chemical changes occur when matter interacts
with heat, light or electricity
and other kinds of matter

Question 10

How are chemical changes represented?

Answer 10

Chemical changes can be represented by word equations.

Question 11

What is a reactant/reactant(s)?

Answer 11

-Found to the left of the
arrow

-Substances present at
the start of the reaction

Question 12

What is a condition/condition(s)?

Answer 12

Found in the middle of the arrow

A condition/condition(s) are Factors (e.g. heat, light and pressure) required for the reaction to take place

Represents order and
direction of the reaction.

Question 13

What is a product/product(s)?

Answer 13

-Found to the right of the
arrow

-Substances present at the
end of the reaction

Question 14

What is an example of a chemical reaction?

Answer 14

Burning charcoal is an example of a chemical reaction.

Question 15

What is the chemical reaction of Burning charcoal?

Answer 15

Carbon and oxygen are the reactants
The condition is heat
and carbon dioxide is the product

Question 16

Do The products of a chemical reaction have different
properties from that of the reactants.

Chemical energy stored in the charcoal is converted to
heat and light energy.

Answer 16

The products of a chemical reaction have different
properties from that of the reactants.
Chemical energy stored in the charcoal is converted to
heat and light energy.

Question 17

How are fireworks displayed in the sky?

Answer 17

• Fireworks display brilliant colours in the sky.
• Different chemical compounds in the fireworks produce the different colours.
• When the compounds are burnt, they undergo chemical reactions to produce an amazing display of light.

Question 18

What is mixing?

Answer 18

-Light sticks are often used during
special occasions.

-The changes within the light stick
is an example of a chemical
change that is produced when
mixing substances.

-A light stick contains two
chemicals that are kept
separate in an external
casing and a smaller, thinner
tube on the inside.

2.
When the stick is bent, the
inner tube breaks and
releases the chemical inside
.
-Mixing substances also produces
other chemical changes.

-Dilute acids produce chemical
changes when mixed with rust.

-We can use this property to remove
rust stains.

Question 19

What is an example of a chemical change during mixing?

Answer 19

Antacids are usually
prescribed for gastric pains.

Gastric pains are felt when
too much gastric juices are
produced in the stomach.

Antacids react with
hydrochloric acid found in
gastric juice to form a
harmless product.

This provides relief for
gastric pains.

Question 20

Elaborate on heating.

Answer 20

When we cook an egg, a chemical
change occurs.

The process is a chemical
change as the reaction is
irreversible.

Heat interacts with different
substances to bring about
many different kinds of
changes.

Question 21

What is thermal decomposition?

Answer 21

Thermal decomposition is a process in which a substance is broken down into two or more simpler substances by the effect of heat.

Question 22

What is an example where thermal decomposition takes place?

Answer 22

Sugar breaks down into carbon and
water vapor when heated for too long.

This process is known as thermal decomposition.

Question 23

What is another example where thermal decomposition take place?

Answer 23

Limestone undergoes thermal decomposition in order
to produce glass.

Limestone is mainly made up of calcium carbonate.

This process is a chemical change as calcium carbonate has interacted with heat to form new products.

Question 24

Elaborate on the interactions between matter and oxygen

Answer 24

When we expose objects such as bicycles and chains to
the environment for a long time, parts of these objects
made of iron or steel may turn rusty.

Such objects become rusty when the iron or steel reacts
with oxygen in the presence of water or moisture.

Rusting is an oxidation process.

Question 25

What is oxidation?

Answer 25

Oxidation is a chemical change in which a substance

reacts with oxygen.

Question 26

When does oxidation occur?

Answer 26

Oxidation also occurs during

– combustion; and

– cellular respiration.