CIE iGCSE Co-Ordinated Science P2.1.3 Pressure changes Exam Style Questions Paper 1
Question
A gas is contained in a cylinder of constant volume.
The gas is cooled.
What happens to the speed of the molecules of the gas and to the pressure of the gas?
▶️Answer/Explanation
Ans: A
Question
A fixed mass of gas is trapped in a cylinder by a piston, as shown. The volume of the gas is increased at constant temperature by moving the piston to the right, as shown.
What effect does this have on the average speed of the molecules and on how many collisions are made by the molecules with the piston each second?
▶️Answer/Explanation
Answer: C
Explanation: When the volume of the gas is increased at constant temperature, the average speed of the gas molecules remains unchanged because temperature is directly related to the average kinetic energy of the molecules. However, the number of collisions with the piston decreases because the molecules are now more spread out, reducing the frequency of collisions. Therefore, the correct answer is C.
Question
A substance is a gas when its temperature is 65°C. How do the boiling point and the melting point of this substance compare with 65°C?
| boiling point | melting point | |
|---|---|---|
| A | above 65°C | above 65°C |
| B | above 65°C | below 65°C |
| C | below 65°C | above 65°C |
| D | below 65°C | below 65°C |
▶️Answer/Explanation
Answer: D
Explanation: If the substance is a gas at 65°C, its boiling point must be below 65°C (since it has already boiled) and its melting point must also be below 65°C (since it is in the gas phase, it has already melted).