Particle model of matter
Density, the states of matter and changes of state, internal energy, specific heat capacity and specific latent heat.
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Particle model of matter, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Calculate density
Density is how much mass is packed into a volume: density = mass ÷ volume, ρ = m/V, in kg/m³ or g/cm³. A block of 240 g and 30 cm³ has a density of 8 g/cm³. Something denser than water sinks in it, which is a handy real-world check.
Describe the three states of matter using the particle model
In a solid, particles are packed close in a fixed pattern and only vibrate. In a liquid they are still close but free to move around each other. In a gas they are far apart and move quickly in all directions. The stronger the forces between particles, the higher the melting and boiling points.
Explain internal energy and changes of state
Internal energy is the total energy stored in the particles of a substance, in their movement and positions. Heating raises it, making particles move faster (a temperature rise) or breaking the forces between them (a change of state). Changes of state are physical, not chemical - the same substance remains, so they can be reversed.
Use specific heat capacity
Specific heat capacity is the energy needed to raise 1 kg of a substance by 1 °C: E = mcΔθ. Water has a high value (about 4200 J/kg°C), so it heats and cools slowly, which is why it is used in radiators. Heating 2 kg of water by 10 °C needs 2 × 4200 × 10 = 84 000 J.
Use specific latent heat
Changing state takes energy without any temperature change, because it goes into breaking forces between particles. Specific latent heat is the energy per kilogram to do this: E = mL. That is why the temperature stays at 0 °C while ice melts - all the energy is spent turning solid into liquid, not warming it.
Explain gas pressure and its link to temperature
Gas pressure comes from particles colliding with the walls of their container. Heating a gas makes the particles move faster, so they hit the walls harder and more often - the pressure rises if the volume is fixed. This is why a sealed can heated in a fire can burst.
Particle model of matter key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Density
- Mass per unit volume: ρ = m/V, measured in kg/m³. It is why the same substance as a gas fills far more space than as a solid.
- Internal energy
- The total kinetic and potential energy of all the particles in a system. Heating a system increases its internal energy.
- Change of state
- Melting, freezing, boiling, condensing or sublimating. A physical change: no new substance forms, mass is conserved, and the change can be reversed.
- Specific latent heat
- The energy needed to change the state of 1 kg of a substance with no change in temperature: latent heat of fusion for melting, of vaporisation for boiling.
- Gas pressure
- The force exerted on the walls of a container by gas particles constantly colliding with them. Heating a gas makes the collisions more frequent and more energetic.
Practice
Try a Particle model of matter question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
A stone has a mass of 1.2 kg and a volume of 400 cm³. Work out its density, in g/cm³. (1 kg = 1000 g.)
- 0.003
- 0.33
- 3
- 480
Show the answer and the working
Answer: 3
Convert the mass to grams first: 1.2 kg = 1200 g, then ρ = 1200 ÷ 400 = 3 g/cm³.
- The volume is in cm³, so the mass must be in grams for a density in g/cm³.
- Convert: 1.2 kg = 1.2 × 1000 = 1200 g.
- ρ = m ÷ V = 1200 ÷ 400 = 3, so the density is 3 g/cm³.