Particle Model & Pressure (Edexcel GCSE Physics)

The particles of a gas exert a pressure on the walls of a container. Which row of the table is correct when the pressure of the gas changes?

Figure 3 shows an oxygen cylinder.

Figure 3

The volume of the gas in the cylinder is 2100 cm³.

When the gas is released into the atmosphere the volume of the gas is 8600 cm³.

The pressure of the atmosphere is 98 kPa.

Calculate the pressure of the gas when it is in the cylinder. Use the equation

pressure of the gas in the cylinder = ........................... kPa

Figure 1 shows some gas particles in a container with a piston which can be moved in or out to change the volume of the gas. 

Figure 1

Add arrows to the diagram to show the random motion of the gas particles. 

Explain how the movement of the particles of gas produces pressure inside the container. 

State the effect on the pressure if you pushed the piston into the container. Assume the temperature does not change.

When the gas in the container is heated, the piston moves outwards.

Describe what happens to the gas particles.

Figure 1 shows a syringe which contains air.

Figure 1

When the piston is pushed in, the volume and pressure in the syringe change.

State how the volume and pressure of the air change when the piston is pushed in.

Use words from the box to complete the following sentences about kinetic theory.

Molecules in a gas are in constant random motion at ............... speeds.

Random motion means that the molecules do not travel in a specific path and undergo sudden changes in their motion if they collide with the ............... of its container or with other ................. .

The ................ of the gas is related to the average kinetic energy of the molecules.

The syringe can be used as a pump to inflate a bicycle tyre where the air inside the tube exerts an outward force on the wall of the tube.

It takes 3.2 litres (l) of air from the atmosphere to inflate the empty tube to a pressure of 360 000 Pa.

Atmospheric pressure is 100 000 Pa.

Calculate the final volume of air inside the tube once inflated.

  final volume = ................................... l

The air in the bicycle pump gets warm when a bicycle pump is used to inflate the tube.

Complete the sentences by circling the correct words:

When the air in the bicycle pump is compressed, the volume / pressure of the gas decreases and the volume / pressure increases.

This is because the particles are moving in less space and collide more often / less often / the same amount.

The increased / decreased pressure leads to an increase in temperature. This is because the temperature is a measure of the average kinetic / potential / thermal energy of particles.

When the air in the bicycle pump is compressed, this increases / decreases the energy in the kinetic / potential / thermal store of the air particles and contributes to the overall kinetic / potential / thermal energy stored in the system, this is why the bicycle pump gets warm.

Figure 1 shows a spray-can containing gas particles which are in constant motion.

Figure 1

Explain how the gas particles cause pressure on the walls of the spray-can.

Liquid leaves the can when the button is pressed.

Describe and explain what happens to the gas pressure in the spray-can as the liquid leaves.

In order to investigate gas pressure further, two balloons are blown up to the same size. One balloon is put in a freezer.

After a while, the two balloons are compared, and it is found that the balloon that has been cooled is smaller. 

Explain why the cooled balloon is smaller using ideas about particles.

A decision is made to investigate the link between temperature and the size of the balloon.

The researcher writes a plan for this experiment:

There are several flaws in the plan.

Identify one of these faults and suggest an improvement to correct it.

Figure 1 shows a fixed mass of gas inside a cylinder with a movable piston.

Figure 1

(i) Describe, in terms of gas particles, how the gas exerts a pressure on the cylinder.

[3]

(ii) Figure 2 shows the same gas squashed into a smaller volume.

Figure 2

State what happens to the pressure the gas exerts on the cylinder when the volume of gas is reduced, as in Figure 2.

[1]

(iii) State what happens to the gas particles when the volume of the gas is reduced, as in Figure 2.

[1]

A digital thermometer gives a temperature reading of 23°C.

Calculate the value of this temperature in kelvin.

A student changes the volume of gas in a container and notes the pressure for different values of the volume.

The results are shown in Figure 6 and plotted on the graph in Figure 7.

Figure 6

Figure 7 

(i) Identify the anomalous result plotted on Figure 7 by drawing a circle on Figure 7 around the anomalous point.

[1]

(ii) Draw the curve of best fit on Figure 7.

[1]

(iii) Describe how the graph in Figure 7 would change if the student repeated the experiment with the same mass of gas, at a higher constant temperature.

[2]

Figure 8 shows a small container of carbon dioxide at high pressure.

The pressure, P₁ , in the container is 8.00 MPa.

The volume, V₁ , of the container is 14.5 cm³.

Figure 8

The container is pierced and all of the carbon dioxide goes into a large balloon.

The volume of gas, V₂ , in the large balloon is 1160cm³.

Calculate the pressure, P₂ , in the large balloon.

Use the equation

P₁V₁ = P₂V₂

pressure in the large balloon = ........................... MPa

Figure 4 shows a small piece of copper about 3 cm high.

Figure 4

A student wants to determine the density of copper.

The student uses a balance to measure the mass of the piece of copper.

i) Explain how the student could measure the volume of the piece of copper.

[3]

ii) The mass of the piece of copper is 0.058 kg.

The volume of the piece of copper is 6.5 × 10^–6 m³.

Calculate the density of copper.

density of copper = ......................................... kg/m³ [2]

A student wants to determine the specific heat capacity of copper.

Figure 5 shows a piece of copper, with a thread tied around it, in a glass beaker of boiling water.

Figure 5

The student leaves the piece of copper in the boiling water so that the copper reaches a temperature of 100°C.

The student uses the thread to take the piece of copper out of the boiling water.

The student puts the hot piece of copper into a different beaker of cold water at 20°C.

The apparatus is shown in Figure 6.

Figure 6

The student assumes that the thermal energy gained by the water equals the thermal energy lost by the piece of copper.

The water and copper both reach a temperature of 22°C.

The cold water gains 1050 J of energy.

The mass of the piece of copper is 0.058 kg.

i) Calculate a value for the specific heat capacity of copper, using these results.

Use the equation

change in thermal energy = mass × specific heat capacity × change in temperature

ΔQ = m × c × Δθ

specific heat capacity of copper from these results = ............ J/kg °C [2]

ii) The value for the specific heat capacity of copper obtained from the student’s results is lower than the correct value.

State two ways that the experiment could be improved to give a value that is closer to the correct value.

[2]

When the pressure in a container of gas increases, the particles of the gas

A student investigates the pressure and volume of some trapped gas.

Figure 4 shows the apparatus used.

Figure 4

Figure 5 shows the student’s table of results.

Figure 5

i) Suggest what the student should add to the headings of the table in Figure 5.

[1]

ii) Use Figure 5 to estimate the volume of gas for a pressure reading of ‘170’.

volume of gas = ..............................................................[2]

iii) Suggest two ways the student could improve the investigation.

1 .......................................................................................

2 .......................................................................................

[2]

iv) Explain whether the values, in the column headed ‘p × V’ in Figure 5, fit the equation

P₁ × V₁ = P₂ × V₂

[3]

Figure 16 shows a metal container with a movable piston.

Figure 16

Point X is on the inner surface of the container. The gas in the container is at a higher pressure than the air outside the container.

Which of these shows the direction of the force, due to the gas, on the container at point X?

The pressure of the gas in Figure 16 (P₁) is 120 kPa.

The volume of the gas in Figure 16 (V₁) is 2500 cm³ The piston is pushed up slowly so that the temperature of the gas does not change.

The new volume of the gas (V₂) is 1600 cm³.

Calculate the new pressure of the gas, P₂. Use the equation

new pressure, P₂= ................................. kPa

Figure 17 shows a bicycle pump with a closed end.

Figure 17

The area of the piston is 2 cm².

A force of 28 N is applied to the piston.

Calculate the pressure, in N/cm², of the piston on the air in the bicycle pump.

pressure = .............................................. N/cm²

A container is sealed so that the mass of the gas inside cannot change.

The volume of the gas is changed and the pressure is measured at different volumes.

The temperature of the gas does not change. Figure 18 is a graph of the results.

Figure 18

Explain, in terms of the movement of particles, why there is a pressure on the container and why the pressure changes as shown in Figure 18.