krit.club logo

Materials and Matter - Evaporation and condensation

Grade 3IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Evaporation is the process where a liquid changes into a gas. This occurs when the liquid is heated, causing molecules like H2OH_2O to move faster and escape into the air.

•

Condensation is the process where a gas turns back into a liquid. This happens when the gas (water vapor) touches a cold surface and loses heat.

•

Water vapor (H2OH_2O in gas form) is invisible. When it condenses, it forms visible droplets.

•

The temperature at which water boils and turns rapidly into gas is 100∘C100^\circ C. However, evaporation can happen slowly at lower temperatures, such as 25∘C25^\circ C.

•

Factors that speed up evaporation include higher temperatures, increased surface area, and wind.

📐Formulae

Liquid+Heat→Gas(Evaporation)Liquid + Heat \rightarrow Gas (Evaporation)

Gas−Heat→Liquid(Condensation)Gas - Heat \rightarrow Liquid (Condensation)

Tboiling=100∘CT_{boiling} = 100^\circ C

Tfreezing=0∘CT_{freezing} = 0^\circ C

💡Examples

Problem 1:

After a rainy day, a puddle of water on the ground disappears even though the temperature is only 20∘C20^\circ C. What process is occurring?

Solution:

The process is Evaporation.

Explanation:

Heat from the sun and the surrounding air gives energy to the H2OH_2O molecules in the puddle, turning them into invisible water vapor in the air.

Problem 2:

When you breathe onto a cold window pane, a thin layer of water forms. Explain why.

Solution:

This is caused by Condensation.

Explanation:

Your breath contains warm water vapor (H2OH_2O). When it hits the cold glass (Tglass<TbreathT_{glass} < T_{breath}), it cools down and turns back into tiny liquid water droplets.

Problem 3:

If you have two containers of water, one at 30∘C30^\circ C and one at 60∘C60^\circ C, which one will evaporate faster?

Solution:

The container at 60∘C60^\circ C will evaporate faster.

Explanation:

Higher temperatures provide more thermal energy, allowing more H2OH_2O molecules to escape the liquid state and become gas.