Topic 14 - Particle Model

Question 1

Describe a solid

Answer 1

Strong forces of attraction hold particles close together in a fixed, regular arrangement. The particles don’t have enough energy in their kinetic energy stores so they vibrate in their fixed positions.

Question 2

Describe a liquid

Answer 2

Forces of attraction between particles are weaker. The particles are closer together, but can move past each other and form irregular arrangements. They have more energy in their kinetic energy stores than the particles in a solid - move in random directions at low speeds.

Question 3

Describe a gas

Answer 3

There are almost no forces of attraction between particles. They have more energy in their kinetic energy stores and are free to move - random directions at high speeds.

Question 4

How do you work out density?

Answer 4

density (kg/m3) = mass (kg) ÷ volume (m3)

Question 5

Describe how to find the density of an object

Answer 5

1) Measure the mass (m1) of the object using a mass balance.
2) Fill the bottle with a liquid of a known density (e.g. water).
3) Place the stopper into the bottle and dry the outside.
4) Measure the mass of the bottle (m2)
5) Empty the bottle and place the object into the density bottle. Repeat steps 2 and 3. Measure the mass of the bottle (m3).
6) Calculate the volume of displaced water:
The mass of the displaced water = m2 - (m3-m1). You know the density of water, so you can use V mp to find the volume displaced. This equals the volume of the object.
7) Calculate the density of the object using p = m ÷ V with the mass you measured in step 1 (m3) and the volume you calculated in step 6.

Question 6

How does density vary with state in a closed system?

Answer 6

The mass of a substance doesn’t change when the state of an object changes state. However, when a substance changes state, its volume also changes. The particles are closer together when they’re a solid than a liquid and closer together when liquid than gas. Therefore the change in volume changes its density - p=mv.

Question 7

When is a substance most dense?

Answer 7

Solid

Question 8

When is a substance least dense?

Answer 8

Gases

Question 9

Why does the mass of a substance stay the same when it changes state?

Answer 9

The mass of a substance is equal to the mass of its particles and as the particles are only being rearranged, the mass doesn’t change. Therefore mass is conserved. Changes in state are a physical change because the material recovers its original properties if the change is reversed.

Question 10

How does heating a system change its energy stores?

Answer 10

The energy in a substance’s thermal energy store is held by its particles in their kinetic energy store. So when you heat a liquid, the extra energy is transferred into the particles’ kinetic energy stores, making them move faster.

Question 11

What does specific heat capacity mean?

Answer 11

The change in energy of a substance’s thermal stores needed to raise the temperature of 1kg of that substance by 1 degrees celsius.

Question 12

What does specific latent heat mean?

Answer 12

Amount of energy needed to change 1kg of it from one state to another without changing its temperature.

Question 13

How do you work out change in thermal energy?

Answer 13

change in thermal energy (J) = mass (kg) × specific heat capacity (J/kg °C) × change in temperature (°C)

Question 14

How do you work out the thermal energy needed for a change in state?

Answer 14

thermal energy for a change of state (J) = mass (kg) × specific latent heat (J/kg)

Question 15

How could houses be insulated to prevented unwanted heat loss?

Answer 15

• Fitting carpets, curtains and draught excluders
• Double glazing. Prevents conduction and convection
• Cavity wall insulation. Blowing insulating material between the brick and the inside wall. Reduces heat loss by conduction
• Loft insulation. Similar to cavity wall insulation.

Question 16

Describe how to measure the specific heat capacity of water. (7)

Answer 16

1) Place one litre (1 kg) of water in the calorimeter.
2) Place the immersion heater into the central hole at the top of the calorimeter.
3) Clamp the thermometer into the smaller hole with the stirrer next to it.
4) Fully insulate the calorimeter by wrapping it loosely with cotton wool.
5) Record the temperature of the water.
6) Connect the heater to the power supply and a joulemeter and turn it on for ten minutes. Stir the water regularly.
7) After ten minutes the temperature will still rise even though the heater has been turned off and then it will begin to cool. Record the highest temperature that it reaches and calculate the temperature rise during the experiment.

Question 17

Evaluate the experiment to measure the specific heat capacity of water. (3 p + E = 6)

Answer 17

> All experiments are subject to some amount of experimental error due to inaccurate measurement or variables that cannot be controlled. In this case, not all of the heat from the immersion heater will be heating up the water, some will be lost to the surroundings.
More energy has been transferred than is needed for the block alone as some is transferred to the surroundings. This causes the calculated specific heat capacity to be higher than for one kilogram (kg) of water alone.
The lid on the calorimeter has reduced much thermal energy loss, and the use of cotton wool insulation has also helped to insulate the calorimeter. Thicker insulation would improve the accuracy of the results even more.

Question 18

Describe how to obtain a graph showing changes in temperature over time for heated ice. (6)

Answer 18

1. Place 50g of crushed ice straight from the freezer into the calorimeter.
2. Place the immersion heater into the central hole at the top of the calorimeter.
3. Clamp the thermometer with its bulb in the ice but near the top of the ice.
4. Record the temperature of the ice.
5. Connect the heater to the power supply and joulemeter, turn it on and record the temperature every 20 seconds.
6. Continue until the thermometer bulb is no longer under the level of the water.

Question 19

Describe pressure in terms of the motion of its particles

Answer 19

As particles are moving quite fast and randomly, collisions occur frequently. The collisions exert a force with whatever they collide with. Therefore a pressure is created due to the Pressure = Force ÷ Area

Question 20

How does the speed of particles depend on the temperature of a gas in a fixed volume?

Answer 20

The higher the temperature, the faster the particles move and the more often they collide with the container. The force exerted by the each particle during a collision also increases as the temperature increases. Therefore increasing pressure.

Question 21

How does changing the volume of a gas in a constant temperature affect pressure?

Answer 21

Increasing the volume of a gas means the particles get more spread out and are less likely to hit the walls of particles. The gas pressure decreases. Pressure and volume are inversely proportional - when volume goes up, pressure goes down.

Question 22

What formula shows the relationship for a gas of fixed mass at a constant temperature?

Answer 22

P1V1 = P2V2

Pressure - Pa (N/m2)
Volume - m3

Question 23

What is absolute zero?

Answer 23

The coldest anything can ever get. This is -273˚c or 0K. The particles have as little energy in their kinetic stores as it’s possible to get - they are pretty much still.

Question 24

How do you convert from degrees Celsius to kelvins?

Answer 24

Add 273

Question 25

How do you convert from kelvins to degrees Celsius?

Answer 25

Subtract 273

Question 26

How can you change the pressure of a gas inside a container(balloon) by heating or cooling?

Answer 26

As the balloon is heated, the gas particles inside it gain energy and move around quicker. This increases the pressure of the gas inside the balloon. The outward pressure of the gas inside the balloon is now larger than the inward pressure caused by the surroundings. The balloon (and so the volume of the gas) expands until the pressures are equal once more. Cooling the gas in the balloon has the opposite effect the outward pressure is smaller than the inward pressure, so the gas inside the balloon is compressed.

Question 27

What do collisions between particles and the wall of a container cause?

Answer 27

A gas exerts a force on its container due to collisions between the particles and the walls of the container. Although, these collisions happen in random directions, they add together to produce an overall fore at right angles to the walls of the container.

Question 28

Why does doing work on a gas can increase its temperature, including a bicycle pump?

Answer 28

The gas exerts pressure on the plunger of the pump, and so exerts a force on it. Work has to be done against this force to push down the plunger. This transfers energy to the kinetic energy stores of the gas particles, so increases the internal energy and therefore the temperature. If the pump is connected to e.g. a tyre, some of this energy is transferred from the gas to the thermal energy store of the tyre, and you’ll feel the tyre getting warmer as you pump it up.