Question

Name the phase change in each of these events: (a) Dew appears on a lawn in the morning. (b) Icicles change into liquid water. (c) Wet clothes dry on a summer day.

Short answer

a) Condensation b) Melting c) Evaporation

Step-by-step solution

Identify Phase Change for Dew

When dew appears on a lawn in the morning, it is due to water vapor in the air condensing into liquid water. The phase change here is called condensation.

Identify Phase Change for Icicles

When icicles change into liquid water, it is due to the ice (solid) melting into water (liquid). The phase change here is called melting.

Identify Phase Change for Drying Clothes

When wet clothes dry, the water in the clothes evaporates into the air. The phase change here is called evaporation.

Key concepts

Condensation

Condensation is the process of water vapor changing into liquid water. This usually happens when warm, moist air cools down. As the air temperature drops, the water vapor in the air cannot hold as much moisture. Thus, the excess water vapor condenses into liquid droplets. Examples of condensation include dew forming on grass in the morning or water droplets collecting on the outside of a cold glass.

- Condensation occurs because cooler air can hold less water vapor than warmer air.
- It’s a critical part of the water cycle, returning water from the atmosphere to the Earth's surface.
- Dew, fog, and mist are common natural occurrences of condensation.

Melting

Melting is when a solid turns into a liquid. This happens when the solid absorbs heat energy. The heat causes the particles in the solid to vibrate more rapidly, eventually breaking free from their fixed positions. The solid then transforms into a liquid. Examples include ice melting into water or chocolate melting in your hand.

- Melting occurs at a specific temperature called the melting point.
- The melting point varies for different substances, for example, ice melts at 0°C (32°F).
- This is an endothermic process, meaning it absorbs heat energy from the surroundings.

Evaporation

Evaporation is the process where liquid water turns into water vapor (gas). It occurs when water molecules at the surface gain enough energy to break free from the liquid. This happens naturally, particularly in warmer temperatures or when exposed to wind. Examples include a puddle drying on a sunny day or wet clothes drying on a summer day.

- Evaporation is a surface phenomenon; only molecules at the surface can evaporate.
- It is a cooling process; as water evaporates, it absorbs heat from its surroundings.
- Factors such as temperature, humidity, and wind speed affect the rate of evaporation.