Topic 14 - Particle Model

• What is the definition of density? State the relevant equation with units.

  ● The mass per unit volume of a material

  ● ⍴=m/v

  ● Density (kg/m³), Mass (kg), Volume (m³)
• What is meant by a state of matter?

  A form in which matter can exist, based on the particle arrangement in a substance.
• Give the different states of matter in order (least to most) of density of atoms.


  ● Least dense: Gas

  ● Liquid

  ● Most dense: Solid
• Use kinetic theory to explain the structure of liquids


  The particles have some kinetic energy. They are free to move and can move around in random directions at very slow speeds.
• Explain the movement of particles in a solid

  The particles vibrate around a fixed position as they do not have enough kinetic energy to move freely.
• Describe the structure of particles in a gas

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

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

  In a change of state, the material can return to having its previous properties if the change is reversed.
• What is the internal energy of a substance?


  ● The energy stored by the particles

  ● The sum of the total kinetic and potential energies that make up the system
• What two things can heating a substance do?

  1. Raise its temperature

  2. Change the state of the substance
• What three factors determine the temperature change of a system?

  1. Mass of substance being heated

  2. Type of material (Specific heat capacity)

  3. Energy inputted into the system
• What is sublimation?


  the process in which a solid changes directly into a gas
• What is the difference between physical changes and chemical changes in substances?

  - physical changes can be reversed

  - chemical changes cannot be easily reversed
• How does heating cause a substance to change state?

  Heating matter gives particles more potential energy. This energy is used to break the bonds of attraction, leading to a change of state.
• Why does heating increase the temperature of substance?

  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.
• State the equation used to calculate the energy change when a substance is heated. Give appropriate units.

  ● ΔE = m c Δ𝛉

  ● Energy (J), Mass (kg), Specific Heat Capacity (J/kg/°C), Temperature (°C)
• Define specific heat capacity

  The energy needed to raise the temperature 1 kg of a material by 1ᵒC
• Define specific latent heat

  The amount of energy needed to change 1kg of a substance from one state to another without changing its temperature
• State the equation for the energy required to change state. Give appropriate units.

  Energy (J) = Mass (kg) x Specific latent heat (J/kg)

  E = mL
• Describe the structure of particles in a gas

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

  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.
• State the equation used to calculate pressure. Give appropriate units.

  Pressure (Pa) = Force (N) / Area (m²)

  P = F / A
• What factor affects the average kinetic energy of gas molecules?

  - The temperature of the substance

  - The higher the temperature, the higher the average kinetic energy of the molecules
• What effect does increasing temperature have on the pressure of a gas when held at constant volume?

  Gas pressure will increase as the temperature increases.
• Why does pressure increase as temperature increases (at a constant volume)?

  ● Kinetic energy of molecules increases

  ● Collisions between molecules becomes more frequent

  ● Greater rate of change of momentum

  ● Greater force and therefore pressure
• 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?

  ● There are more collisions per second in gas B than in gas A

  ● The rate of collisions is higher in B
• Describe the force that the pressure of a gas exerts on the walls of its container.

  ● The net force acts at right-angles to

  the container's surface

  ● The force increases as pressure

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

  ● Molecules become more spread out and so time

  between collisions increases

  ● This reduces the rate of collisions

  ● Rate of change of momentum decreases, and so

  force exerted on container decreases, resulting in

  a lower pressure
• What can be said about the product of pressure and volume for a fixed mass of gas at a constant temperature?

  It is constant.

  p V = constant
• What is the unit used for pressure?

  Pascal (Pa)
• What increases when you do work on a gas?

  ● The internal energy of the gas

  ● This can also lead to an increase of

  temperature
• How do you convert between Celsius and Kelvin?

  K = C + 273

  C = K - 273
• What is absolute zero?

  -273 degrees Celsius

  Particles have no kinetic energy and do not move
• What equation can be used to calculate the pressure/volume for a gas for which the mass is fixed and temperature is constant?

  P₁ × V₁ = P₂ × V₂
• Why does the temperature of air inside a bike pump increase when it is pumped?

  ● Work is done on a gas when it is compressed

  ● Doing work on a gas increases its internal energy, so also increases the average kinetic energy of the molecules

  ● Temperature increases with an increase of average kinetic energy