Topic 3: Particle Model of Matter

Question 1

What 2 things can the particle model be used to explain?

Answer 1

1. Density
2. Three states of matter

Question 2

Properties of a solid [3]

Answer 2

1. Strong forces of attraction hold the particles close together in a fixed, regular arrangement
2. Particles don’t have much energy so can only vibrate about their fixed positions
3. The density is the highest

Question 3

Properties of a liquid [3]

Answer 3

1. Weaker forces of attraction so particles are close together, but can move past each other, and form irregular arrangements
2. More energy - move in random directions at low speeds
3. Less dense than solids

Question 4

Properties of a gas [3]

Answer 4

1. Almost no forces of attraction between particles
2. The most energy - free to move and travel in random directions at high speeds
3. Less dense than liquids

Question 5

Why is mass conserved when a substance changes state?

Answer 5

The number of particles doesn’t change, just their arrangement

Question 6

Why is a achange of state said to be a physical change? [2]

Answer 6

1. You don’t end up with a different substance - its the same substance in a different form
2. If you revserse the change, the substance will return to its original form and get back its original properties

Question 7

What is internal energy?

Answer 7

The total kinetic and potential energy of all the particles that make up a system

Question 8

Internal energy

How does heating an object change its state? [3]

Answer 8

1. Heating an object transfers energy to the kinetic energy store of the particles
2. When the particles have enough energy in their kinetic energys stores, they can break the bonds holding them together
3. This causes a change of state

Question 9

What is specific latent heat?

Answer 9

The amount of energy required to change the state of 1kg of a substance with no temperature change

Question 10

What is the specific latent heat of fusion?

Answer 10

Change of state from solid to liquid

Question 11

What is the specific latent heat of vaporisation?

Answer 11

Change of state from liquid to gas

Question 12

Change of state occuring

What is happening on the flat parts of a heating graph? [3]

Answer 12

1. A substance is melting or boiling
2. Energy is still being put in so the internal energy is still increasing
3. However, the energy is being used to break the bonds between the particles rather than raising the temperature

Question 13

Change of state occuring

What is happening on the flat parts of a cooling graph? [3]

Answer 13

1. A substance is condensing or freezing
2. Bonds are forming between the particles which releases energy and decreases the internal energy
3. However, the temperature doesn’t go down until all of the substance has condensed or frozen

Question 14

Explain how colliding gas particles create pressure in a sealed container [3]

Answer 14

1. As gas particles move at high speeds, they bang into each other and anything else that gets in the way
2. When they collide with something they exert a force
3. This force is pressure

Question 15

Explain how increasing the temperature of gas particles in a fixed volume increases pressure [3]

Answer 15

1. Increasing the temperature, increases the speed of the particles
2. This leads to more frequent collisions
3. This leads to increased net force, and so gas pressure

Question 16

Explain how increasing the volume in which a gas in contained at a fixed temperature decreases pressure [3]

Answer 16

1. Particles become more spread out
2. They hit the walls of the container less often
3. The net force decreases, and so the gas pressure

Question 17

Explain why a helium balloon expands if released into the atmosphere [3]

Answer 17

1. Atmospheric pressure decreases with height
2. So the pressure outside the balloon decreases
3. This causes the balloon to expand until the pressure inside drops until it is the same as the atmospheric pressure

Question 18

What can doing work on a gas cause and why?

Answer 18

An increase in temperature due to an increase in internal energy

Question 19

Explain how doing work on a bicyle pump leads to an increase in gas temperature [4]

Answer 19

1. Gas applies pressure to the plunger of the pump, exerting a force on it
2. Work has to be done against this force to push the plunger down
3. This transfers energy to the kinetic energy store of the gas particles
4. Increasing the temperature