1.6 More changes of state
Summary: Look at Figure 1. What happens to the water if you use a hairdryer to dry your hair? It changes state from liquid to gas without boiling. This is evaporation. You can use the particle model to… Tags: science oxford-science student-book-7 chemistry Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
- compare the before and after states of evaporating, condensing, and subliming
- describe what happens to the particles in a substance when it evaporates, condenses, and sublimes
- compare what happens to the particles in a substance when it evaporates and boils.
Think back
- Give two properties of a substance in the liquid state.
- Name the starting and finishing states in boiling.
- Why is mass conserved in boiling?
Key idea When a substance evaporates, it changes state from liquid to gas. Evaporation happens below the melting point. Condensation is the change of state from gas to liquid. Sublimation is the change of state from solid to gas.
Key word evaporation, evaporating, condensing, condensation, subliming, sublimation
Look at Figure 1**. What happens to the water if you use a hairdryer to dry your hair? It changes state from liquid to gas without boiling. This is evaporation. You can use the particle model to explain evaporation.**
Figure 1When you use a hairdryer to dry your hair, the water evaporates.
Explaining evaporation
In a liquid, some particles have more Energy than others. The particles with most energy leave the surface of the liquid. Then they move away from the liquid. The particles spread out, forming a gas. The liquid has evaporated. The mass stays the same because all the particles still exist - they have just moved.
A substance can change from the liquid to the gas state by evaporating or boiling. Table 1 shows some differences between these two processes. Table 1 differences between evaporating and boiling. Process
How particles leave the liquid
Temperature
Does the mass change?
evaporating
particles escape from the liquid surface
happens at any temperature
no
boiling
bubbles of the substance form everywhere in the liquid, they rise to the surface and escape
happens only at the boiling point
no
A Give two differences between evaporating and boiling.
How is evaporating useful?
The person in Figure 2 is sweating. Why do you sweat? Sweating cools you down by evaporation. Sweat comes out of pores in your skin. Water from the sweat then evaporates. The water particles need energy to move away as a gas. They take this energy from your skin. This cools you down.
Why is it quicker to dry your hair with a hairdryer? The hairdryer speeds up evaporation in two ways. It transfers energy to help particles leave the liquid surface. It also moves water particles that have just evaporated away from your hair.
Figure 2Sweat helps to cool you down by evaporation.
What is condensing?
Is the inside of your bedroom window ever wet after a cold night? At bedtime, water particles in the room were mixed with air particles. The water particles were far apart, as a gas. During the night, the water particles hit the cold glass of the window. They moved closer to other water particles, until they were touching. They continued to move, but they stopped moving everywhere in the room and started to move over each other.
The changes in the arrangement and movement of the particles resulted in liquid water. This change of state from gas to liquid is called condensing or condensation. It can happen at any temperature below a substance’s boiling point.
B Name the starting and finishing states in condensing.
What is subliming?
Where does stage smoke come from? It comes from solid carbon dioxide. Carbon dioxide is solid at temperatures below -78.5°C. At this temperature and above, solid carbon dioxide changes state to become a gas. Carbon dioxide does not normally exist as a liquid. This change of state from solid to gas is called subliming or sublimation. Water particles from the air condense around carbon dioxide particles. Tiny drops of liquid water form. It is this liquid water that you see as stage smoke (see Figure 3).
Figure 3Water particles from the air condense around carbon dioxide particles to make stage smoke.
C Give the state of carbon dioxide at room temperature (20 °C).
Literacy skills Use the Glossary at the back of this book to find out the meanings of the key words. Then write each word in a sentence.
Stretch zone
- Write five correct sentences using the sentence starters and enders below. Sentence startersIn boiling …In condensing …In evaporating …In subliming … Sentence enders… particles leave from the surface of a liquid.… particles change from the solid to the gas state.… substances change from the liquid to the gas state.… particles leave from all parts of a liquid.… substances change from the gas to the liquid state.
- Describe the changes in the movement and arrangement of particles when a substance condenses.
Stretch zone
- Name the process that occurs when: puddles dry upa glass of very cold water gets wet on the outside.