14. Particle Model

Question 1

What is the definition of density? State the unit.

Answer 1

The mass per unit volume of a material.
Unit: kg/m³

Question 2

What is meant by a state of matter?

Answer 2

A form in which matter can exist, based on the particle arrangement in a substance.

Question 3

Give the different states of matter in order of increasing density of atoms (lowest to highest).

Answer 3

least —> most
gas, liquid, solid

Question 4

Use kinetic theory to explain the structure of liquids.

Answer 4

The particles have some kinetic energy. They are free to move and can move around in random directions at very slow speeds.

Question 5

Explain the movement of particles in a solid.

Answer 5

The particles vibrate around a fixed position as they do not have enough kinetic energy to move freely.

Question 6

Describe the structure of particles in a gas.

Answer 6

Particles in a gas have almost no forces between them therefore they are completely free to move, and move at high speeds in random directions.

Question 7

What is always conserved when a substance undergoes a change of state?

Answer 7

Mass

Question 8

How does a change of state differ from a chemical change?

Answer 8

In a change of state, the material can return to having its previous properties if the change is reversed.

Question 9

What is the internal energy of a substance?

Answer 9

• The energy stored by the particles.
• The sum of the total kinetic and potential energies that make up the system.

Question 10

What two things can heating a substance do?

Answer 10

• Raise its temperature.
• Change the state of the substance.

Question 11

What three factors determine the temperature change of a system?

Answer 11

• Mass of substance being heated.
• Type of material (specific heat capacity)
• Energy inputted into the system.

Question 12

What is sublimation?

Answer 12

When a solid turns directly into a gas.

Question 13

What is the difference between physical changes and chemical changes in substances?

Answer 13

Physical changes can be reversed, chemically changes cannot be easily reversed.

Question 14

How does heating cause a substance to change state?

Answer 14

Heating matter gives particles more potential energy. This energy is used to break the bonds of attraction, leading to a change of state.

Question 15

Why does heating increase the temperature of a substance?

Answer 15

It increases the amount of thermal energy in that substance. It also gives the particles more kinetic energy, meaning they move faster and their temperature increases.

Question 16

Define specific heat capacity.

Answer 16

The amount of energy needed to increase the temperature of 1kg of a substance by 1⁰C.

Question 17

Define specific latent heat.

Answer 17

The amount of energy needed to change the state of 1kg of a substance with no change in temperature.

Question 18

Explain the pressure of a gas in terms of the motion of particles.

Answer 18

The particles move in random directions. When they collide with the walls of a container they exert a force which acts at a right angle to the container. This causes pressure.

Question 19

What factor affects the average kinetic energy of gas molecules?

Answer 19

• The temperature of the gas.
• The higher the temperature, the higher the average kinetic energy of the molecules.

Question 20

What effect does increasing temperature have on the pressure of a gas when held at constant volume?

Answer 20

Gas pressure will increase as the temperature increases.

Question 21

Why does pressure increase as temperature increases (at a constant volume)?

Answer 21

• Kinetic energy of molecules increases.
• Collisions between molecules becomes more frequent.
• Greater rate of change of momentum.
• Greater force and therefore pressure.

Question 22

If gas A is at a low pressure, and gas B is at a high pressure, what can be said about the rate of collisions in each gas?

Answer 22

• There are more collisions per second in gas A than in gas B.
• The rate of collisions is higher in A.

Question 23

Explain how increasing the volume of a gas results in a decrease of pressure.

Answer 23

• Molecules become more spread out so rate of collision decreases.
• Rate of change of momentum decreases, and so force exerted on container decreases, resulting in a lower pressure.

Question 24

What is the unit used for pressure?

Answer 24

Pascal (Pa)

Question 25

How do you convert between degree celsius and kelvin?

Answer 25

Kelvin (K) to degrees celsius (⁰C) = +273
Degrees celsius (⁰C) to kelvin (K) = -273

Question 26

What is absolute zero?

Answer 26

-273⁰C
Particles have no kinetic energy and do not move.