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5 Solids, liquids and gases

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  1. Solids, liquids and gases units

    1. Use the units degree Celsius (°C), kelvin (K), joule (J), kilogram (kg), kilogram per cubic metre (kg/m³), metre (m), square metre (m²), cubic metre (m³), metre per second (m/s), metre per second squared (m/s²), newton (N) and pascal (Pa).

    2. Use the unit joule per kilogram degree Celsius, J/(kg °C).

  2. (b) Density and pressure

    1. Know and use density = mass ÷ volume, ρ = m/V.

    2. Practical: investigate density using direct measurements of mass and volume

    3. Know and use pressure = force ÷ area, p = F/A.

    4. Understand how the pressure at a point in a gas or liquid at rest acts equally in all directions

    5. Know and use pressure difference = height × density × gravitational field strength, p = hρg.

  3. (c) Change of state

    1. Explain why heating a system will change the energy stored within the system and raise its temperature or produce changes of state

    2. Describe the changes that occur when a solid melts to form a liquid, and when a liquid evaporates or boils to form a gas

    3. Describe the arrangement and motion of particles in solids, liquids and gases

    4. Practical: obtain a temperature–time graph to show the constant temperature during a change of state

    5. Know that specific heat capacity is the energy required to change the temperature of an object by one degree Celsius per kilogram of mass (J/kg °C)

    6. Use change in thermal energy = mass × specific heat capacity × change in temperature, ΔQ = mcΔT.

    7. Practical: investigate the specific heat capacity of materials including water and some solids

  4. (d) Ideal gas molecules

    1. 5.15Gas pressure

      Explain how molecules in a gas have random motion and that they exert a force, and hence a pressure, on the walls of a container

    2. 5.16Absolute zero

      Understand why there is an absolute zero of temperature, which is –273 °C

    3. 5.17Kelvin scale

      Describe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scales

    4. 5.18Temperature and gas molecule speed

      Understand why an increase in temperature results in an increase in the average speed of gas molecules

    5. 5.19Kelvin temperature and kinetic energy

      Know that the Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules

    6. 5.20Gas pressure relationships

      Explain, for a fixed amount of gas, the qualitative relationship between: • pressure and volume at constant temperature • pressure and Kelvin temperature at constant volume

    7. 5.21Pressure-temperature relationship

      Use p₁/T₁ = p₂/T₂ for the pressure and kelvin temperature of a fixed mass of gas at constant volume.

    8. 5.22Pressure-volume relationship

      Use p₁V₁ = p₂V₂ for the pressure and volume of a fixed mass of gas at constant temperature.