Particle model of matter

Question 1

Describe density

Answer 1

The amount of stuff in something!
density = mass divided by volume

and the units are kg/m3

Question 2

How can you calculate the density of an irregular object?

Answer 2

To find the volume put it into a measuring cylinder of water and measure the difference in cm3 weigh it to find the mass.
Dont forget to check if the answer needs to be in kg/m3

Question 3

Describe the particle arrangement in a solid

Answer 3

The particles are fixed in a regular pattern held together by strong forces.
They cannot move but can vibrate so a solid maintains it’s shape.

Question 4

Describe the particle arrangement in a liquid

Answer 4

The particles are held together by bonds which are weaker than those in a solid.
The particles can move across each other but stay in contact. This means that a liquid flows and changes shape to fit in a container.

Question 5

Describe the particle arrangement in a gas

Answer 5

The particles in a gas are separated by a relatively large distance and the bonds between the particles are very weak.
The particles move in a constant random motion and can fill any space.

Question 6

What is meant by the term internal energy

Answer 6

It is a combination of the kinetic and potential energy of all of the particles in a system.

Question 7

Explain the effects of heating a system

Answer 7

1. Heating increases the temperature which increases the kinetic energy of the atoms or molecules.
2. The molecules in a gas or liquid can move more quickly.
3. The bonds between the particles can break down causing a change of state, solid-> liquid-> gas

Question 8

Identify and describe the different changes of state

Answer 8

1. melting- solid turns to liquid- internal energy of the system increases
2. freezing- liquid turns to solid- internal energy of the system increase
3. boiling or evaporation- liquid turns to gas-internal energy of the system increases
4. Condensation- gas turns to liquid- internal energy of the system increase
5. Sublimation - solid turns directly into gas- internal energy of the system increases

Question 9

What is a change of state?

Answer 9

It is a physical change of the substance.
The substance remains the same- it doesnt become a different substance.
It is reversible
It does not cause a change in mass

Question 10

Define specific heat capacity

Answer 10

The amount of energy required to heat 1kg of a substance by 1 degree C

Question 11

What are the variables when the temperature of a system is increased by adding energy?

Answer 11

1. The mass of the substance
2. The type of material
3. the energy being put into the system

Question 12

What is the equation to calculate the change in thermal energy

Answer 12

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

Question 13

Give two examples of the importance of the high specific heat capacity of water

Answer 13

1. Humans bodies are composed mainly of water, this means that we do not heat up too much when we exercise or cool down when it is cold
2. Hot water is used to keep many of our homes warm, the high specific heat capacity means that the water doesn’t cool down quickly as if flows around the system and it can transfer a lot of heat energy.

Question 14

Define specific latent heat

Answer 14

the amount of energy required to change the state of a substance with no change in temperature
energy required for a change of state = mass x specific latent heat
measured in J/kg
when a change of state occurs the energy being supplied changes the internal energy but not the temperature

Question 15

Describe the difference between the specific latent heat (slh) of fusion and the slh of vaporisation

Answer 15

The slh of fusion is the amount of energy required to change 1kg of solid into a liquid at the same temperature
The slh of vaporisation is the amount of energy required to change 1kg of liquid into a gas (vapour) at the same temperature

Question 16

Describe how you could carry out an experiment to measure the latent heat of vapourisation of water

Answer 16

1. Place a beaker of water on a heat proof mat on a balance. Measure the mass - 968g (0.968kg)
2. A joulemeter is connected.
3. The water is brought to the boil and the joulemeter is then set to 0.
4. After boiling the water for 5 minutes the following measurements are taken
   * joulemeter reading - 60kJ (60,000J)
   * the mass of the water and beaker - 944g (0.944kg)
   E = m x L
   60000 = (0.986-0.944) x L
   L = 60000 / 0.024
   L = 25000000J/kg

Question 17

Explain why a cooling graph may have a plateau- straight line- instead of a constant curve

Answer 17

If the substance changes state as it cools there may be a period of a few minutes where the temperature remains constant instead of dropping steadily.
This happens because the substance releases energy as the internal energy of its molecules decrease. When it has all solidified the temperature starts falling again.

Question 18

Describe the main points of the particle model of gases

Answer 18

1. The molecules or atoms in a gas are in a constant state of random motion.
2. The particles collide with each other and with the wall of a container without losing any of their kinetic energy
3. The temperature of the gas is related to the average kinetic energy of the molecules.
   As the kinetic energy of the molecules increases so does the temperature of the gas.

Question 19

Explain the term gas pressure

Answer 19

As the molecules of a gas bounce off their container they exert a force on the wall. The molecules will rebound off the wall at all sorts of angles but the force exerted on the wall will always be at right angles to the wall,
If the temperature of a gas inside a container increases then the average speed of the particles increases and they hit the walls of the container with more force. Therefore the gas pressure increases.