A Journey through States of Water · Lesson 4 of 8
How Heating and Cooling Change Water
“Connect melting, freezing, evaporation, and condensation in one state-change model.”
• Name and explain melting, freezing, evaporation, and condensation. • Describe how heating or cooling can change the state of water. • Trace a route through all three states without treating water as a new substance. • Recognise changes of state in wax and coconut oil.
Change the conditions, change the state
An ice cube taken from a freezer becomes liquid water. Water in a freezer can become ice. Liquid water can also become vapour, and vapour can form liquid drops on a cold surface. In each case, the substance is water; heating or cooling changes its state. Think of these changes as linked paths rather than four unrelated words.
Between solid and liquid
When ice receives enough heat from its surroundings, it melts into liquid water. Cooling liquid water sufficiently in a freezer can make it freeze into solid ice. The direction matters: melting goes from solid to liquid, whereas freezing goes from liquid to solid.
The change of a solid into a liquid.
The change of a liquid into a solid.
Problem
Some candle wax near a flame becomes liquid and later turns solid again. Name both changes.
- 1.Heat supplied near the flame changes solid wax to liquid wax: melting.
- 2.As liquid wax loses heat and cools, it becomes solid wax: freezing or solidification.
- 3.The example shows that changes of state are not limited to water.
Coconut oil may appear more solid during a cool winter and liquid again when warmer. Do not assume that every material changes state at the same temperature as water. The important pattern here is that heating and cooling can cause changes of state in different substances.
Between liquid and gas
Liquid water can evaporate into water vapour. This can happen from a surface at room temperature; it is not necessary to boil all the water. When vapour meets a cooler surface and forms liquid drops, condensation has occurred. Evaporation and condensation lead in opposite directions between the liquid and gaseous states.
Use the diagram as a route map. From ice to vapour through the liquid state, first melt the ice, then evaporate some liquid water. To return, vapour condenses to liquid and liquid freezes to ice. The chapter’s diagram-completion task asks you to supply the states and process names in their correct positions.
“Ice and water” does not tell you whether the process is melting or freezing. Identify the starting state and the ending state before choosing a process name.
Problem
Vapour forms droplets on a cold surface. The droplets then freeze. Describe the two changes.
- 1.Gas to liquid is condensation: vapour becomes droplets.
- 2.Liquid to solid is freezing: the droplets become ice.
- 3.Both changes move toward a solid state as cooling continues.
Quiz
What change is called melting?
What is the reverse of freezing along the ice–water path?
Which sequence takes ice through liquid water to vapour?
Droplets form from vapour on a cool lid. Which process took place?
Why is candle wax a useful comparison?
Practice Problems
- Draw and label arrows between ice, liquid water, and water vapour for all four changes.
- Describe what happens to water placed in a freezer and to the resulting ice left on a table.
- Trace the two-step route from water vapour to ice through liquid water.
- Use candle wax to explain the difference between melting and freezing.
- Why is it incorrect to call droplets forming on a cold lid evaporation?
- Give a winter example involving coconut oil and identify the change when it warms again.
Key Takeaways
• Melting and freezing connect solid and liquid states in opposite directions. • Evaporation and condensation connect liquid and gaseous states in opposite directions. • Heating and cooling can change a substance’s state without changing its identity.