5 Solids, liquids and gasses

5.01 use the following units: degree Celsius (°C), Kelvin (K), joule (J), kilogram (kg), kilogram/metre3 (kg/m3), metre (m), metre2 (m2), metre3 (m3), metre/second (m/s), metre/second2 (m/s2), newton (N) and pascal (Pa)

The units for:

temperature: degree Celsius (°C) or Kelvin (K)

Energy: Joule (J)

mass: Kilogram (kg)

density: kilogram/metre cubed (kg/m3)

distance: metre (m)

area: metre squared (m2)

volume: metre cubed (m3)

velocity: metre per second (m/s)

acceleration: metre per second squared (m/s2)

force: newton (N)

pressure: pascal (Pa)

5.02 use the following unit: joules/kilogram degree Celsius (J/kg °C)

the unit for 

specific heat capacity: joules/kilogram degree Celsius (J/kg °C) 

5.03 know and use the relationship between density, mass and volume:

Units of density depend on units used for mass and volume:

E.g. mass in [g] and volume in [cm3] gives density in [g/cm3], however mass in [kg] and volume in [m3] gives density in [kg/m3].

5.04 practical: investigate density using direct measurements of mass and volume

  • The density of an object can be found by measuring the mass and volume and applying the formula above to calculate the density.
  • For a regular object use a ruler to measure the lengths needed to determine the volume.
  • For an irregular object submerge it in water and measure the displaced volume.
  • Measure the mass of either type of object using a measuring balance.

5.05 know and use the relationship between pressure, force and area:

pressure (Pa) = force (N)/ area (m2

  • Pressure is defined as force per unit area.
  • One pascal (Pa) is equivalent to one N/m2

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

Pressure in liquids:

Pressure in liquids acts equally in all directions as long as the liquid is not moving.

5.07 know and use the relationship for pressure difference: p = h × ρ × g

Pressure difference [Pa] = Density [kg/m3] x g [N/kg] x Height [m]

ΔP = ρ g h

  • The equation can be used in liquids or gases provided you know their densities.

P1 – Patm = ρ g h

P1 = ρ g h + Patm

5.08 explain why heating a system will change the energy stored within the system and raise its temperature or produce changes of state

5.09 describe the changes that occur when a solid melts to form a liquid, and when a liquid evaporates or boils to form a gas

5.10 describe the arrangement and motion of particles in solids, liquids and gases


  • Tightly packed
  • Held in fixed pattern
  • Vibrate about fixed positions


  • Tightly packed
  • Can slide over each other


  • Very spread out
  • Move with rapid, random motion


5.11 practical: obtain a temperature–time graph to show the constant temperature during a change of state

  1. Remove the boiling tube of stearic acid from
    the water bath
  2. Place the tube into a beaker of room
    temperature water
  3. Add a separate thermometer to the water
  4. Take readings from the thermometer in the
    stearic acid and the water every minute
    [Make sure to avoid parallax error while doing so]
  5. Note readings in the table below
  6. Note on the table when you observe the stearic
    acid change from a liquid to a solid.
  7. Plot your results in a graph

5.12 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)

Specific heat capacity:

  • Amount of heat energy required to increase the temperature of 1kg of a substance by 10
  • Unit J/kg 0C

5.13 use the equation: change in thermal energy: ΔQ = m × c × ΔT

Change in thermal energy [J] = Mass [kg] x Specific heat capacity [J/kg 0C] x Change in temperature [0C] 

5.14 practical: investigate the specific heat capacity of materials including water and some solids

  1. Set up the apparatus as shown the diagram.
  2. Make note of all measurements: current (A), potential difference (V), mass (kg).
  3. Use the electronic balance to measure the mass of your
  4. Record the initial temperature of you block.
  5. Switch on the heater and start your stopwatch.
    [You will now leave the heater on for 10 minutes]
  6. While the heater is switched on take readings from the
    Ammeter and the Voltmeter.
  7. Use these to calculate the Thermal Energy that will be
    supplied to the block in 10 minutes
  8. Record the temperature of your block after 10 minutes.
  9. Calculate the Change in Temperature

5.15 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

Gas laws:

  • Gas molecules have rapid and random motion.
  • When they hit the walls of the container, they exert a force.
  • Pressure = Force/Area

5.16 understand why there is an absolute zero of temperature which is –273 °C

Absolute zero:

  • At absolute zero the particles have no thermal energy or kinetic energy, so they cannot exert a force.
  • Absolute zero = 0 Kelvin = -2730C

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

0 K = -273 0C

E.g.         100K = -1730C

                2000C = 473K

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

As you increase the temperature of a gas, the kinetic energy of the gas particles increases and thus their average speed also increases.

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

The Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules.

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

  • As you heat the gas, the kinetic energy of the particles increases, and thus so does their average speed.
  • This means more collisions per second with the walls, and they exert a larger force on the wall.
  • This causes in the total pressure being exerted by the particles to rise.
  • If temperature is constant, the average speed of the particles is constant.
  • If the same number of particles is placed in a container of smaller volume they will hit the walls of the container more often.
  • More collisions per second means that the particles are exerting a larger force on the wall over the same time, so average force exerted on the walls has increased.

5.21 use the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume:

P1/T1 = P2/T2

*Temperature must be in Kelvin

Temperature law:

For a fixed mass of gas at constant volume, the pressure is directly proportional to the Kelvin temperature

5.22 use the relationship between the pressure and volume of a fixed mass of gas at constant temperature:

P1V1 = P2V2

Boyle’s law:

For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume.

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Section 1: Principles of chemistry

      a) States of matter

      b) Atoms

      c) Atomic structure

     d) Relative formula masses and molar volumes of gases

     e) Chemical formulae and chemical equations

     f) Ionic compounds

     g) Covalent substances

     h) Metallic crystals

     i) Electrolysis

 Section 2: Chemistry of the elements

     a) The Periodic Table

     b) Group 1 elements: lithium, sodium and potassium

     c) Group 7 elements: chlorine, bromine and iodine

     d) Oxygen and oxides

     e) Hydrogen and water

     f) Reactivity series

     g) Tests for ions and gases

Section 3: Organic chemistry

     a) Introduction

     b) Alkanes

     c) Alkenes

     d) Ethanol

Section 4: Physical chemistry

     a) Acids, alkalis and salts

     b) Energetics

     c) Rates of reaction

     d) Equilibria

Section 5: Chemistry in industry

     a) Extraction and uses of metals

     b) Crude oil

     c) Synthetic polymers

     d) The industrial manufacture of chemicals

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