Do Now 4 marks Mark scheme Boiling and

Do Now – 4 marks

Mark scheme

Boiling and evaporation Learning today • What is evaporation • How to increase the rate of evaporation. • Condensation • Boiling

Solids, liquids and gases

Internal Energy This is the sum of the kinetic energies - from motion of the particles and potential energies due to forces between the molecules in a substance If you imagine the forces between particles as a spring, you can see if the particles are pulled apart or squashed together that energy is stored in the spring. Similarly there is potential energy between the particles in a substance.

Temperature is a measure of the average random kinetic energy of the particles in a substance. Note that they are not all travelling at the same speed.

Melting? • Changes in kinetic energy and potential energy?

Evaporation? • Changes in kinetic energy and potential energy?

Condensing? • Changes in kinetic energy and potential energy?

Freezing? • Changes in kinetic energy and potential energy? • What is happening

Boiling and evaporation

Evaporation Consider a beaker of water at room temperature

Evaporation The molecules of water are moving around at different speeds, some fast, # of molecules at some slow. a particular speed Average speed of molecule (m/s)

Evaporation If a molecule is at the surface, and moving fast enough, it may escape the liquid. This is called evaporation. Freedom!

Evaporation Since the average speed of the remaining molecules must now be lower, the temperature of the liquid drops (since temperature is a measure of the kinetic energy of the molecules). Freedom!

Evaporation – Please copy If a molecule is at the surface, and moving fast enough, it has enough energy to break bonds and escape the liquid. This is called evaporation. It can happen at any temperature and as it is the molecules with the greater KE escaping the temperature of the liquid reduces. Freedom!

Evaporation If a molecule is at the surface, and moving fast enough, it has enough energy to break bonds and escape the liquid. This is called evaporation. It can happen at any temperature and as it is the molecules with the greater KE escaping the temperature of the liquid reduces. Freedom!

Evaporation If a molecule is at the surface, and moving fast enough, it has enough energy to break bonds and escape the liquid. This is called evaporation. It can happen at any temperature and as it is the molecules with the greater KE escaping the temperature of the liquid reduces. Freedom!

Evaporation can thus take place at any temperature.

Increasing the rate of evaporation Increasing the temperature.

Increasing the rate of evaporation Increasing the temperature means that more molecules are moving fast enough to escape.

Increasing the rate of evaporation Increasing the surface area

Increasing the rate of evaporation Increasing the surface area means that more molecules are at the surface.

Increasing the rate of evaporation Increasing the air flow over the surface

Increasing the rate of evaporation Increasing the air flow over the surface so that molecules are carried away before they can fall back into the liquid

Increasing the rate of evaporation Decreasing the humidity of the surrounding atmosphere

Increasing the rate of evaporation Decreasing the humidity of the surrounding atmosphere to stop water molecules from the atmosphere entering the liquid.

please copy Evaporation can be increased by – Increasing temperature – more particles have a higher KE – Increasing the surface area – more particles closer to the surface – Increasing air flow above the surface – gives the particles somewhere to go to • - Evaporation and Condensation. flv

Boiling and evaporation

Boiling occurs when vapour is produced in the body of the liquid.

Boiling The bubble contains only water vapour, not air! Boiling occurs when vapour is produced in the body of the liquid.

Boiling – Please copy The bubble contains only water vapour, not air! Boiling occurs when vapour is produced in the body of the liquid. This only happens at the boiling point of the liquid.

To summarize: Evaporation takes place only at the surface of the liquid and can take place at any temperature.

To summarize: Boiling means bubbles! Boiling occurs when vapour is produced in the body of the liquid. This only happens at the boiling point of the liquid.

Evaporation -3 marks

Markscheme

Homework – 1. Finish Draw these sentences 2. Stick in all your loose worksheets by Sunday 12 th February 3 Java Lava Power

Homework • If I give you homework you will do it • I will give you a blue slip if you do not

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