PSLE Science Chemistry Topics 1

Question 1

Which of the following is an example of a chemical change?

Accepted Answer

Wood burning to produce ash and smoke

Answer

Burning wood produces ash and smoke — entirely new substances are formed, which is the defining feature of a chemical change.

Question 2

What term describes the process when water vapour cools and turns back into liquid water?

Accepted Answer

Condensation

Answer

Condensation is the process where water vapour loses heat energy and changes back into liquid water.

Question 3

Which state of matter has both a definite shape and a definite volume?

Accepted Answer

Solid

Answer

Solids have tightly packed particles that give them a fixed shape and volume that does not change with the container.

Question 4

Which of the following is NOT a physical change?

Accepted Answer

Iron rusting when exposed to water

Answer

Iron rusting is a chemical change because a new substance — iron oxide (rust) — is formed.

Question 5

When a solid changes directly into a gas without passing through the liquid state, this process is called:

Accepted Answer

Sublimation

Answer

Sublimation is when a solid turns directly into a gas — dry ice (solid carbon dioxide) is a classic example.

PSLE Practice Test