Change of State: Answers

Compare the energy of the particles in a solid, liquid and a gas.

Particles in a solid have a very low amount of energy. Particles in a liquid have a moderate amount of energy and the particles in a gas have a high amount of energy.

Why does evaporation on a liquid’s surface cause the remaining liquid to cool down?

Only the fastest (and therefore hottest) molecules are able to evaporate from the surface of a liquid. When they evaporate this reduces the average kinetic energy (and also the average temperature) of the remaining liquid molecules. Therefore evaporation causes the liquid to cool down.

What is the difference between boiling and evaporation?

Boiling involves the whole liquid whereas evaporation only occurs on the surface of a liquid. Evaporation also happens at lower temperatures than the liquid’s boiling point.

What happens to the temperature of a substance as it changes state? Why does this happen?

The temperature of a substance as it changes state remains constant. This happens because the heat energy is being used to break intermolecular forces between the particles. Therefore, the heat energy is used up rather than being used to raise the temperature of the substance.

Explain how you would carry out an experiment to investigate how the temperature of water changes as it is converted from a solid to a liquid to a gas.

I would place some ice into a beaker and record its temperature using a thermometer. I would them gently heat the beaker using a Bunsen burner, recording the temperature every 20 seconds. I would continue to record the temperature until the water starts to boil. I can then plot a graph of temperature against time.

Define specific heat capacity.

Specific heat capacity is the energy needed to increase the temperature of 1 kg of a substance by 1 degree Celsius.