Aseel Samaro

Understanding evaporation

Have you ever thought about what happens to the water particles when a puddle is left in the sunshine, or to the water produced when you sweat?

The answer is the water has evaporated.

What does this actually mean and how is it different from boiling?

Introduction

If you spill some water on a surface and leave it in the sunshine, after a few hours the water particles will no longer be present and there is no sign of the spill.

The water has evaporated.

The water particles have gained sufficient energy from their surroundings to become a gas.

Examples of evaporation

When clothes are hung out to dry, the air particles in the wind transfer energy by movement (kinetic energy) to the water particles in the clothes.

These gain enough energy to change from a liquid into a vapour.

Smells from perfumes are also an example of evaporation.

The perfume particles gain enough energy by heat from the body, or by kinetic energy from air particles, to become a vapour.

Describe one other example of evaporation.

Where does the energy needed for evaporation to take place come from?

Evaporation occurs at any temperature between the melting point of a liquid and its boiling point.

It happens only at the surface of the liquid.

Some of the surface particles gain enough energy from the surroundings from heat, or from kinetic energy, to leave the surrounding particles in the liquid and become a vapour.

Over time, all the particles at the surface will evaporate.

Differences between boiling and evaporation

Is evaporation more likely to take place at temperatures near the boiling point or near the melting point? Explain your answer.

it will take place near the boiling pointthe temperature is higher, so there is more heat transferred to the liquid particles; so more will evaporate

What are the main differences between boiling and evaporation?Boiling is where the whole of the liquid changes to a gas at a fixed temperature.

Evaporation is where some of the particles escape to become a gas; at temperatures between the melting point and the boiling point

Four factors that affect evaporation are:1. Wind speed: in faster winds, air particles have more kinetic energy. More energy can therefore be transferred to the evaporating particles of the liquid.

Factors affecting evaporation

2. Temperature: at higher temperatures, more energy can be transferred to the particles of the liquid by heat.

3. Surface area: evaporation occurs at the surface of a liquid.With a larger surface area, more energy can be transferred to the particles in the liquid from the surroundings.

4. Strength of the intermolecular forces: some liquids, such as alcohol, have weaker intermolecular forces than others, such as water.

Therefore, with the same amount of energy transferred from the surroundings, more alcohol particles than water particles will escape as a gas.

Explain the factors that affect the rate of evaporation in this process.

The more heat transferred by the Sun the higher the rate of evaporation.

The larger the surface area the higher the rate of evaporation.

The stronger the surface wind the higher the rate of evaporation.

Which of the factors above are likely to have the biggest effect on the rate of

evaporation? Explain your answer.The effect of temperature; the energy

transferred by heat will directly affect the kinetic energy of more surface particles; changing the

state from liquid to gas more quickly.

salt production

Evaporation from oceans accounts for 80 per cent of water delivered as precipitation (rain, snow).

Did you know…?

Thank you