Gases All Around
Learn
There is a third state of matter all around you right now - gas! Even though you cannot see most gases, they are everywhere. Let us learn about this invisible form of matter!
What Is a Gas?
A gas is matter that spreads out to fill any space. Gases have no definite shape AND no definite size!
The air you breathe is made of gases. You cannot see air, but it is there!
Properties of Gases
- No definite shape - fills any container
- No definite size - spreads out or squeezes together
- Usually invisible - you cannot see most gases
- Very light - gases weigh much less than solids or liquids
- Moves freely - gas particles move in all directions
Examples of Gases
Gases are all around us:
- Air - the mixture of gases we breathe
- Oxygen - the gas we need to live
- Carbon dioxide - the gas we breathe out
- Helium - the gas that makes balloons float
- Water vapor - water as a gas (steam)
How Gases Fill Space
Imagine opening a bottle of perfume in one corner of a room. Soon you can smell it everywhere!
That is because gases spread out to fill ALL the space available. The perfume gas traveled through the air to every part of the room.
The Three States of Matter
| Solid | Liquid | Gas |
|---|---|---|
| Own shape | Container's shape | Fills all space |
| Can be held | Needs container | Needs closed container |
| Example: rock | Example: water | Example: air |
Air Takes Up Space
Even though you cannot see air, it takes up space! Here is how you can tell:
- A balloon gets bigger when you blow air into it
- An empty glass pushed into water traps air inside
- Wind is moving air that can push things
Worked Examples
Example 1: Identifying a Gas
Problem: Is the air in a balloon a solid, liquid, or gas?
Step 1: Does air have its own shape? No, it fills the balloon.
Step 2: Can you pour air? No, but it spreads out to fill space.
Step 3: Can you see it? No, it is invisible.
Answer: Gas - Air is a gas that fills the balloon and gives it shape.
Example 2: Proving Air Exists
Problem: How can you prove air is real if you cannot see it?
Evidence 1: Feel the wind blow - that is moving air!
Evidence 2: Blow up a balloon - air takes up space inside.
Evidence 3: Wave your hand fast - you feel air pushing back.
Answer: Even though we cannot see air, we can feel it and see what it does!
Example 3: Water in Three States
Problem: How can water be a solid, liquid, AND gas?
As a solid: Ice! When water gets very cold, it freezes.
As a liquid: Regular water that you drink and swim in.
As a gas: Steam or water vapor - when water gets very hot!
Answer: The same matter (water) can be in different states depending on temperature!
Example 4: Gases Spread Out
Problem: Mom bakes cookies. You are in your bedroom. Soon you smell cookies. Why?
Think: The cookie smell is tiny bits of gas in the air.
Answer: Gases spread out to fill all available space. The cookie smell (gas particles) spread from the kitchen through the whole house until they reached your nose!
Example 5: Comparing States
Problem: Sort these: ice cube, steam, water, rock, juice, helium
Solids: ice cube, rock - They have their own shape.
Liquids: water, juice - They take the shape of their container.
Gases: steam, helium - They spread out to fill space.
Practice Problems
Practice what you learned about gases!
Problem 1: What are the three states of matter?
Show Answer
Solid, liquid, and gas
Problem 2: Can you see most gases?
Show Answer
No - Most gases are invisible, but they are still there!
Problem 3: What gas do we breathe in to live?
Show Answer
Oxygen - We need oxygen to breathe and stay alive.
Problem 4: What makes a balloon float?
Show Answer
Helium gas - Helium is lighter than air, so it floats up!
Problem 5: Is steam a solid, liquid, or gas?
Show Answer
Gas - Steam is water as a gas. It spreads out in the air.
Problem 6: What happens to a gas when you open its container?
Show Answer
The gas spreads out into the room. It does not stay in the container!
Problem 7: Does a gas have a definite shape?
Show Answer
No - Gases have no definite shape. They spread out to fill any space.
Problem 8: Name something that proves air exists.
Show Answer
Examples: wind blowing, balloons filling up, feeling air when you wave your hand, bubbles underwater
Problem 9: What is the air we breathe made of?
Show Answer
Air is a mixture of gases, mainly nitrogen and oxygen.
Problem 10: How is a gas different from a liquid?
Show Answer
A liquid takes the shape of its container but keeps the same amount. A gas spreads out to fill ALL the space in a container - it has no definite size!
Check Your Understanding
Question 1: What is a gas?
Show Answer
A gas is matter that has no definite shape and no definite size. It spreads out to fill any space available.
Question 2: How do gases move?
Show Answer
Gas particles move freely in all directions. They spread out to fill all available space. That is why smells can travel across a room!
Question 3: How can the same matter (like water) be in different states?
Show Answer
Temperature changes the state of matter. Cold water becomes ice (solid). Hot water becomes steam (gas). The matter is the same, but the state changes!
Question 4: Why do we need to keep a lid on soda bottles?
Show Answer
Soda has a gas (carbon dioxide) that makes the bubbles. Without a lid, the gas escapes into the air because gases spread out. The soda goes flat!
Next Steps
- Observe: Notice signs of air - wind, bubbles, smells spreading
- Experiment: Try trapping air underwater with a cup
- Think: How would life be different without gases?
- Challenge: Find examples of matter changing states