States of Matter — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. What happens to the particles of a substance when it is heated?
A) They stop moving completely
B) They move faster and spread apart
C) They stick together more tightly
D) They shrink in size
Adding heat gives particles more energy, causing them to vibrate and move faster. As they speed up, they push apart from each other, which is why heated substances expand or change state.
2. Which is the best example of evaporation?
A) Snow piling up on a driveway
B) A glass of water getting warm
C) Wet clothes drying on a line
D) An ice cube sitting in a freezer
Wet clothes drying on a line shows evaporation because the liquid water in the clothes absorbs heat from the sun and turns into water vapor, a gas that floats away into the air.
3. Why can you smell cookies baking from another room?
A) The cookie particles are solids that roll through the air
B) Gas particles from the cookies spread through the air
C) The oven pushes liquid cookie smell to you
D) Sound waves carry the smell to your nose
When cookies bake, tiny gas particles carrying the cookie smell spread out through the air in every direction. Gas particles move freely and travel from room to room, which is why the smell reaches you.
4. A glass of ice water has water droplets forming on the outside. Why?
A) Water leaks through the glass
B) The ice is melting on the outside
C) Water vapor in the air condenses on the cold glass
D) The glass is sweating because it is nervous
The cold glass cools the warm water vapor in the surrounding air. When that gas cools enough, it condenses and turns back into tiny liquid water droplets on the outside of the glass.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Water boils at 100 degrees Celsius and turns into steam.
Water reaches its boiling point at 100 degrees Celsius. At that temperature, the liquid water has enough energy to change into steam, which is water in the gas state.
2. When particles slow down and pack together, a liquid becomes a solid.
As a liquid loses heat, its particles slow down and move closer together until they lock into fixed positions. Once they are packed tightly in place, the substance becomes a solid.
3. The amount of space an object takes up is called its volume.
Volume measures how much space something takes up. A basketball has a larger volume than a tennis ball because it fills more space.
4. A gas can be compressed into a smaller space by pushing its particles closer.
Gas particles have lots of empty space between them, so you can squeeze them into a smaller area. This is how air gets packed tightly inside a bicycle tire or a basketball.
5. Snow is frozen water, which means it is in the solid state.
Snow is made of ice crystals, and ice is frozen water. Since freezing turns liquid water into a solid, snow is water in its solid state.