2.1 There are three states of matter

Learning intentions

By the end of this topic, you will be able to: • describe the three states of matter • identify the processes that change substances from one state to another.

Figure 1 Solid water (ice) floats on liquid water.

Figure 2 Honeycomb is a combination of solid and gas. Or is it?

Key ideas

• All things are made of matter. • There are three major states of matter – solid, liquid and gas. • Many substances can be found in more than one state.

Solids, liquids and gases

Ice = solid

Water is a common substance that we experience in different states of matter. Solid water is called ice, we drink and wash with liquid water, and the gas form of water is known as water vapour. Occasionally we see a fog or mist in the air. This steam-like substance is actually very small drops of water mixed with the air. Although the ocean and iceberg shown in Figure 1 may look and behave very differently, they are both different forms of water. The ocean is liquid water, and the iceberg is solid water. There is also water vapour in the air. Clouds and fog are made of small liquid water droplets. All of these different states of water are made of the same ‘building blocks’ or water particles. Often, substances can be described as just one state. However, some substances contain more than one state of matter, like honeycomb (Figure 2). Sometimes we can see all the states in the one mixture – like in the glass of iced soda water in Figure 3 – and sometimes it can be diffi cult to tell the state of a mixture. For example, would you classify slime or jelly (Figure 4) as a solid, a liquid or a gas?

Figure 3 A glass of iced soda water contains the three states of matter. Drink = liquid Bubbles = gas (carbon dioxide)DRAFT

Figure 4 Is jelly a solid, a liquid or a gas?

Change of state

The minimum temperature required to melt a solid is called its melting point. Any substance above its melting point will be a liquid (or a gas), and any substance below its melting point will be a solid.

The process of water becoming a gas (water vapour) is called evaporation. Each substance has a different temperature that causes the gas to form. This temperature is called the boiling point. If heat is removed from the water vapour, the gaseous water slows its movement until it once again forms liquid water. This process is called condensation. Figure 9 shows how the state of water changes when heat is added and removed. Figure 5 A kettle boils liquid water.DRAFT

evaporation a change in state from liquid to gas; also a technique used to separate dissolved solids from water

boiling point the temperature at which a liquid boils and becomes a gas

condensation the cooling down of gas into a liquid

Figure 6 Liquid water. When most of us think of water, we think of the liquid form that comes out of our taps. Liquid water sits at the bottom of cups and flows smoothly over surfaces. Water can fit into containers of all shapes and sizes. It is flexible. Figure 7 Solid water. When heat is removed from liquid water, the movement of the water slows. The water has been solidified. This is the solid form of water called ice. Like all solids, ice holds its shape even when it is tipped from a container.

Figure 8 Gas water. When heat is added to liquid water, the water starts to move faster. Eventually it becomes a gas called water vapour. The gas has much more energy than a liquid or solid. It does not sit at the bottom of a container. Instead, it moves freely around the whole container.

Melting point is the temperature at which a solid changes to a liquid (melting). Add heat energy

Boiling point is the temperature at which a liquid changes to a gas (evaporation).

Melting

0°C

Freezing Boiling

100°C

Condensing

Solidi cation (or freezing) is when a liquid changes to a solid.

Preventing evaporation Understanding how water evaporates (liquid to gas) becomes very important when you live in a hot and dry climate like in parts of Australia. Bright sunshine, high temperatures and wind will all cause waterholes to quickly dry up. Before Europeans colonised Australia, First Nations peoples would cover the waterholes in rocks to prevent evaporation.

If water was found in clay, First Nations peoples would make the hole deeper but not wider so that more water could be stored without increasing the evaporation from the water surface. The Yankuntjatjara peoples in the Everard Range region of South Australia would also prevent evaporation by adding sand to their local waterholes. The water particles were able to ‘hide’ between the sand grains, preventing evaporation. When it was time to collect the water, a hole was made in the centre of the sand so that the fresh water could drain into a puddle. Describing matter The properties of a substance are the characteristics that make it unique. Solids, liquids and gases have unique properties. Solids

Figure 9 Adding or removing heat energy can change the state of water.

do not change their shape easily and cannot be compressed. Liquids cannot be compressed, but they can change their shape to fit the physical property container holding them. Gases completely a property of a substance fill the container holding them and can be that can be measured compressed into a smaller space. or observed without Some substances are important to us changing the substance into something else; because of particular properties. For example, examples are colour and one property of water is that it can be used to boiling point dissolve (mix with) many other substances. This makes water useful for cleaning clothes, chemical property cooking and experiments in a chemistry how a substance behaves laboratory. in a chemical reaction, such as how it reacts with The properties of substances can be divided an acid into two groups: 1 Physical properties are what we can observe and measure without changing the substance into something else. Examples of physical properties are colour, texture, boiling point, density and how much heat it can store (heat capacity). Table 1 lists the physical properties of water. 2 Chemical properties are what a substance does in a chemical reaction. Examples include bubbling, permanent colour change and permanent change of state.

Condensation occurs when a gas changes to a liquid. Remove heat energy (cool down) Table 1 Physical properties of water Physical property Value

Melting point 0°C

Boiling point 100°C

Colour Colourless

Density 1.00 g/mL at 25°C

DRAFT

Figure 10 You can sometimes see condensation when you breathe out on a cold morning. The water vapour in your breath becomes a fine liquid when it hits the cold air, making what is commonly called ‘dragon breath’. Retrieve 1 Identify the: a melting point of water b boiling point of water. 2 Use the information in Table 2 below to identify which substance has the: a lowest melting point b highest melting point c lowest boiling point d highest boiling point. Table 2 Melting and boiling points

Substance Melting point (°C) Boiling point (°C)

Water 0 100

Iron 1535 2750

Lead 327 1750

Mercury –39 357

Table salt 805 1413

Oxygen –219 –183

Nitrogen –210 –196

5 Explain what is meant by a ‘property’ of a substance. 6 Explain why the properties of matter are so important to us. Analyse 7 Compare (describe the similarities and differences between) the processes of melting and boiling. 8 Contrast (describe the differences between) the physical and chemical properties of a substance. 9 Categorise the following substances as a solid, liquid or a gas (or a combination of states). ice cream, chocolate bar, clouds, thick smoke, glass, honey, cake or bread, mashed potato, paper, peanut butter (smooth), cling wrap, play dough, sand, steam, slime 10 Classify each of the following properties as either a physical or a chemical property: the ability to 2.1 Check your learning DRAFT be hammered into fl at sheets (malleability), the ability to explode, the amount of vapour released at different temperatures. 11 Identify what would happen to liquid water when heat is applied. Apply

3 Select a common substance, such as cling wrap or vinegar. Name some of the physical properties of this substance.

Comprehend

12 A student claimed a frozen drink bottle was leaking because condensation had formed on the outside of the container. Develop an explanation for the student that describes where the condensed water came from.

4 Describe what happens to water when it: a evaporates b condenses c freezes.

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