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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. 5.3Density equation

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

    2. 5.4Density practical

      Practical: investigate density using direct measurements of mass and volume

    3. 5.5Pressure equation

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

    4. 5.6Pressure in fluids

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

    5. 5.7Pressure difference equation

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

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

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

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

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

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