Particle Model & Pressure Flashcards

All 16 cards in this deck

How do the molecules of a gas move?

In constant random motion — in random directions and with a range of speeds.

True or false? All the molecules in a gas move at the same speed.

False. The molecules move with a range of speeds, in random directions.

What property of the molecules of a gas is the temperature of the gas related to?

The average (mean) kinetic energy of the molecules — the higher the temperature, the greater the average kinetic energy.

What causes the pressure that a gas exerts on the walls of its container?

Molecules colliding with the walls — each collision exerts a force, and pressure is the total force per unit area.

In which direction does the force produced by the pressure of a gas act on the wall of its container?

At right angles (90°) to the wall or surface.

Heating a fixed mass of gas at constant volume increases its pressure. What three changes to the molecules explain this?

1. Higher mean kinetic energy, so higher mean speed
2. More frequent collisions with the walls (more per second)
3. Greater force in each collision, so greater force on the same area

What equation links the pressure and volume of a fixed mass of gas held at a constant temperature?

$pV = \text{constant}$, with pressure $p$ in pascals (Pa).

What are the steps to find the new pressure of a fixed mass of gas at constant temperature when its volume changes?

e.g. $100\,000$ Pa of gas in $0.030$ m$^3$ is compressed to $0.025$ m$^3$

1. Find the constant: $100\,000 \times 0.030 = 3000$
2. Substitute the new volume: $p \times 0.025 = 3000$
3. Rearrange: $p = 3000 \div 0.025 = 120\,000$ Pa

Increasing the volume of a fixed mass of gas at constant temperature decreases its pressure. What happens to the collisions to explain this?

1. Collisions with the walls become less frequent (more time between collisions)
2. So the average force on the walls is lower
3. Pressure is the total force per unit area, so pressure falls

True or false? For a fixed mass of gas at constant temperature, doubling the volume doubles the pressure.

False. The pressure halves — pressure and volume are inversely proportional ($pV = \text{constant}$).

What shape is the graph of pressure against volume for a fixed mass of gas at constant temperature?

A curve falling from left to right (inverse proportion); a graph of $p$ against $\frac{1}{V}$ is a straight line through the origin.

In an investigation of how the pressure of the air in a syringe varies with its volume, what are the independent, dependent and control variables?

Independent: volume of the gas. Dependent: pressure of the gas. Control: temperature of the gas and mass of gas.

In physics, what is work?

The transfer of energy by a force.

What happens to a gas when work is done on it?

Its internal energy increases, which can cause an increase in its temperature.

Why does the air inside a bicycle pump get hotter when the plunger is pushed in quickly?

The force on the plunger does work on the enclosed gas, transferring energy to it, so its internal energy and temperature increase.

True or false? The temperature of a gas can rise even when it is not heated by a hotter object.

True. Doing work on the gas, e.g. compressing it quickly, increases its internal energy and can raise its temperature.