OCR GCSE Combined Science: Physics: Matter

The particle model describes a substance as being made of tiny particles arranged and moving differently in the three states of matter.

Describe how the arrangement, spacing and movement of the particles differ in a solid, a liquid and a gas, and explain, using the particle model, why a solid has a fixed shape but a gas fills its container and is easily compressed. (6 marks)

A solid metal block has a mass of 810 g and a volume of 300 cm³.

(a) Calculate the density of the metal in $\text{g/cm}^3$g/cm3. Use $\rho = \dfrac{m}{V}$ρ=Vm​. Show your working and give the unit. (3 marks)

(b) A different sample of the same metal has a volume of $100\ \text{cm}^3$100 cm3. State its density and give a reason for your answer. (1 mark)

A kettle heats 0.50 kg of water. The specific heat capacity of water is $4200\ \text{J/kg}^\circ\text{C}$4200 J/kg∘C.

(a) Calculate the energy needed to raise the temperature of the water from $20^\circ\text{C}$20∘C to $100^\circ\text{C}$100∘C. Use $E = mc\Delta\theta$E=mcΔθ. Show your working and give the unit. (2 marks)

(b) State one reason why, in practice, the kettle must supply more energy than your answer to part (a). (1 mark)

An ice cube at its melting point is warmed until it has completely melted into water. The specific latent heat of fusion of water is $3.34 \times 10^5\ \text{J/kg}$3.34×105 J/kg. The mass of the ice is 0.020 kg.

(a) Calculate the energy needed to melt the ice completely. Use $E = mL$E=mL. Show your working and give the unit. (2 marks)

(b) State what happens to the temperature of the ice–water mixture while it is melting. (1 mark)

A fixed amount of gas is sealed in a rigid container. The gas is then heated, so the temperature of the gas increases while its volume stays the same.

Explain, using the particle model, why the pressure of the gas increases when it is heated. (2 marks)

When a sealed flask of water is left in sunlight, some of the liquid water evaporates into water vapour, but the total mass of the sealed flask and its contents does not change.

State the name of the principle that explains why the total mass stays the same. (1 mark)