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States of Matter - Evaporation and condensation in the water cycle

Grade 5IGCSE

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

🔑Concepts

The Water Cycle is the continuous movement of H2OH_2O through the Earth and its atmosphere involving changes in state.

Evaporation: This is the process where liquid H2OH_2O gains thermal energy (heat) and changes into a gas called water vapor. It occurs faster when the temperature increases.

Condensation: This is the process where water vapor (gas) loses heat energy and changes back into liquid H2OH_2O. In the atmosphere, this leads to the formation of clouds.

The Sun is the primary energy source that drives the cycle by providing the heat necessary for evaporation.

Transpiration: A specific type of evaporation where H2OH_2O is released from the leaves of plants into the atmosphere as gas.

Precipitation: When H2OH_2O droplets in clouds become too heavy, they fall back to Earth as rain, snow, or hail.

📐Formulae

ightarrow Gas \text{ (Evaporation)}$$
ightarrow Liquid \text{ (Condensation)}$$

H2O (Liquid)H2O (Gas)H_{2}O \text{ (Liquid)} \rightleftharpoons H_{2}O \text{ (Gas)}

💡Examples

Problem 1:

Explain why a wet cloth dries faster on a sunny day than on a cloudy day using the concept of H2OH_2O states.

Solution:

The cloth dries faster due to an increased rate of evaporation.

Explanation:

On a sunny day, the thermal energy from the Sun is higher. This heat energy is absorbed by the liquid H2OH_2O in the cloth, allowing the molecules to move faster and transition into the gas state (water vapor) more quickly.

Problem 2:

You notice small droplets of H2OH_2O forming on the inside of a window on a cold morning. Identify the process and the energy change involved.

Solution:

The process is Condensation.

Explanation:

Warm water vapor inside the house hits the cold surface of the glass window. The gas loses heat energy to the cold glass, causing the H2OH_2O molecules to slow down and cluster together, changing back into liquid droplets.

Problem 3:

In an experiment, 100ml100ml of H2OH_2O is boiled. What happens to the mass of the liquid in the beaker?

Solution:

The mass of the liquid H2OH_2O decreases.

Explanation:

As heat is applied, the H2OH_2O reaches its boiling point and undergoes a state change from liquid to gas (H2O(l)H2O(g)H_2O_{(l)} \rightarrow H_2O_{(g)}). The water vapor escapes into the air, leaving less liquid in the beaker.