SP14 - Particle Model

Question 1

What is kinetic theory?

Answer 1

The theory that states that everything is made of tiny particles, which move to determine its state.

Question 2

Describe the properties of a solid

Answer 2

Forces of attraction hold particles closely together. The particles can vibrate but cannot move around. Therefore, solids keep their shape and cannot be compressed.

Question 3

Describe the properties of liquids.

Answer 3

The particles are moving faster, so the forces of attraction between the particles are not strong enough to keep them in fixed positions. The particles can move past each other, so liquids can flow and take the shape of their container. The particles are still very close together, so liquids generally cannot be compressed.

Question 4

Describe the properties of gases.

Answer 4

The particles are far apart and move around quickly. They are compressible and expand to fill their container.

Question 5

Explain why a change of state is a physical change.

Answer 5

During a change of state, the particles end up in a different arrangement, but no new substances are formed and the substance recovers its original properties if the change is reversed.

Question 6

What is density?

Answer 6

The density of a substance is the mass of a certain volume of the substance.

Question 7

What is the equation for density?

Answer 7

Density = mass/volume
P=m/V

Question 8

What is generally true about the densities of solids, liquids and gases?

Answer 8

Almost all substances are most dense when they are solids and least dense when they are gases. A solid is usually denser than the same substance as a liquid, because the particles in a solid are closer together. Water/ice is an exception to this.

Question 9

Core practical - investigating densities

Answer 9

Liquids:
- place an empty beaker on a balance and set the balance to zero
- use a measuring cylinder to measure 50cm3 of the liquid and pour it into the beaker. Write down the reading on the balance. This is the mass of 50cm3 of the liquid
Solids:
- find the mass of the solid and write it down
- for a regular shape, you can measure the volume using bxwxh
- for an irregular shape, stand a displacement can on a bench with its spout over a bowl. Fill it with water until the water just starts coming out if the spout
- hold a measuring cylinder under the spout and carefully drop the object into the can. If it floats, carefully push it down until all of it is submerged. Your fingers should not touch the water
- stand the measuring cylinder on the bench and read the volume of water you have collected. This is the same as the volume of the object. Wrote it down
- use density = mass/volume

Question 10

What is thermal energy?

Answer 10

The energy stored in the movement of particles that make up the substances in a system. It is transferred to the system by heating.

Question 11

What is temperature?

Answer 11

It is a measure of the movement of particles (when a solid stores more thermal energy, the vibrations of its particles increase, the speeds of particles in liquids or gases increase when the liquid or gas is storing more energy).

Question 12

What does the amount of thermal energy stored in something depend on?

Answer 12

• its temperature
• its mass
• the material it’s made from

Question 13

What is specific heat capacity?

Answer 13

The amount of energy it takes to increase the temperature of 1kg of the substance by 1 degrees C.

Question 14

Why does temperature remain constant when a substance being heated is changing state?

Answer 14

The extra energy supplied to the substance is being used to overcome the forces between particles and change the state, not to increase the temperature.

Question 15

What is specific latent heat?

Answer 15

The amount of energy it takes to make 1kg of a substance change state.

Question 16

What is the equation for specific heat capacity?

Answer 16

Change in thermal energy (J) = mass (kg) x specific heat capacity (J/kg degrees C) x change in temperature (degrees C)

Question 17

What is the equation for specific latent heat?

Answer 17

Thermal energy needed for a change of state (J) = mass (kg) x specific latent heat (J/kg)

Question 18

Core practical - investigating water

Answer 18

Melting ice:
- put a boiling tube full of crushed ice into a Pyrex (or heatproof) beaker. Put a thermometer in the ice and note the temperature
- put the beaker onto a tripod and gauze. Pour hot water from a kettle into the beaker, and keep it warm using a burden burner.
- measure the temperature of the ice every minute and record your results in a table. Stop taking readings three minutes after all the ice has melted.
Specific heat capacity:
- put a polystyrene cup in a beaker onto a battery-powered balance and zero the balance. Fill the cup almost to the top with water and write down the mass of the water. Remove the cup from the balance
- put a thermometer and a 12V electric immersion heater into the water, making sure the heating element is completely below the water level. Connect the immersion heater to a joulemeter
- record the temperature of the water, then switch the immersion heater on. Stir the water in the cup gently using the thermometer
- after five minutes write down the temperature of the water again and write down the reading on the joulemeter

Question 19

What is the temperature of a gas?

Answer 19

A measure of the average kinetic energy of the particles in the gas. The faster the average speed of the part lies, the higher it’s temperature. Heating a gas increases the kinetic energy of the particles, so they move faster and the temperature rises.

Question 20

What causes the pressure in a gas?

Answer 20

The pressure of a gas is due to the forces on the walls of the container caused by the moving particles hitting the walls.

Question 21

How can the pressure of a gas be increased?

Answer 21

Either by heating the gas (particles move more quickly and so collide with the walls of the container more forcefully and more frequently) or reducing the volume of the container the gas is in (a smaller container means more particle collision with the walls so a greater force is exerted on the walls overall).

Question 22

What is the equation for pressure?

Answer 22

Pressure (Pa) = Force (N) / area (m^2)

Question 23

What is absolute zero?

Answer 23

-273 degrees C. It is the temperature at which if a gas could be made this cold, it’s pressure would be zero and the particles would not be moving.

Question 24

What is the Kelvin temperature scale?

Answer 24

It measures temperatures relative to absolute zero. The units are Kelvin (K) and 1K is the same temperature interval as 1 degrees C. Absolute zero is 0K on this scale.

Question 25

How do you convert between Kelvin and Celsius?

Answer 25

To convert from Kelvin to degrees Celsius, subtract 273. To convert from degrees Celsius to Kelvin, add 273.

Question 26

What is the relationship between average kinetic energy of particles in a gas and kelvin temperature of the gas?

Answer 26

Directly proportional

Question 27

What is gas pressure?

Answer 27

The force acting at right angles to the walls of a container due to collisions of particles with the walls of the container.

Question 28

At which angle to particles exert a force on container walls?

Answer 28

90 degrees (right angles)

Question 29

Which equation shows the relationship between the volume and pressure of a fixed mass of gas at constant temperature?

Answer 29

P1 x V1 = P2 x V2

The product of the initial pressure and volume is equal to the product of the final pressure and volume.

Question 30

Why does the temperature of a gas increase as it’s pressure increases?

Answer 30

As the pressure increases, the particles collide with the walls of the container more frequently. The particles are moving more quickly, which is detected as an increase in temperature.

Question 31

Why does a bicycle pump get warm as you use it?

Answer 31

Each time you push the pump handle, the force is transferring energy to the gas inside the pump. As the piston of the bicycle pump moves, the speed of any particles inside it will increase when they bounce off it. The average speed of the particles inside the pump will increase, and we detect this as an increase in temperature.