Changes of State and Internal EnergyAQA GCSE Physics: Flashcards

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Define internal energy.

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Define internal energy.: Internal energy is the total kinetic and potential energy of all the particles in a substance.
How does heating a substance affect its internal energy?: Heating increases the internal energy of a substance by increasing either the kinetic energy of the particles (raising temperature) or the potential energy of the particles (during a change of state).
Define melting.: Melting is the change of state from solid to liquid. Particles gain kinetic energy and break free from fixed positions, but their average kinetic energy (temperature) remains constant during the process.
Define freezing.: Freezing is the change of state from liquid to solid. Particles lose kinetic energy and form fixed structures, but the temperature remains constant during the process.
Define evaporation.: Evaporation is the change of state from liquid to gas. Particles gain kinetic energy and escape from the liquid surface. Temperature remains constant during the process.
Define condensation.: Condensation is the change of state from gas to liquid. Particles lose kinetic energy and form a liquid. Temperature remains constant during the process.
Define sublimation.: Sublimation is the change of state directly from solid to gas without passing through the liquid state. Particles gain sufficient energy to escape as a gas.
Why does temperature remain constant during a change of state?: During a change of state, the energy supplied (heat) is used to overcome the forces between particles and increase their potential energy, not to increase their kinetic energy. This means temperature (which depends on average kinetic energy) does not change.
What is latent heat?: Latent heat is the energy required to cause a change of state at constant temperature. It is the energy needed to break or form bonds between particles without changing the temperature.
State the equation for calculating energy during a change of state.: Q = mL, where Q is energy in joules (J), m is mass in kilograms (kg), and L is specific latent heat in joules per kilogram (J/kg).
Define specific latent heat of fusion.: Specific latent heat of fusion is the energy required to change 1 kilogram of a solid into a liquid at constant temperature, or the energy released when 1 kilogram of liquid freezes into a solid.
Define specific latent heat of vaporisation.: Specific latent heat of vaporisation is the energy required to change 1 kilogram of a liquid into a gas at constant temperature, or the energy released when 1 kilogram of gas condenses into a liquid.
Which requires more energy: melting or evaporation? Explain why.: Evaporation requires more energy than melting. This is because particles must completely escape the attractive forces of other particles to form a gas, whereas during melting particles only need to overcome some of these forces to form a liquid.
A student heats ice. Explain what happens to the internal energy during the melting process.: During melting, the internal energy increases because particles gain potential energy as bonds between them are broken. The temperature remains constant, so kinetic energy does not increase.
Calculate the energy needed to evaporate 2.5 kg of water. (Specific latent heat of vaporisation of water = 2,260,000 J/kg): Q = mL = 2.5 × 2,260,000 = 5,650,000 J (or 5.65 MJ)