States of Matter — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Which state of matter has a definite volume but takes the shape of its container?
A) Solid
B) Liquid
C) Gas
D) Plasma
Solids hold their own shape, gases spread out to fill any space, and plasma is not part of these everyday three states. Only a liquid keeps the same amount of matter while flowing to match whatever container is holding it.
2. What happens to water when it is heated to its boiling point?
A) It freezes into ice
B) It stays the same
C) It evaporates into water vapor
D) It becomes heavier
At the boiling point, water gets so hot that its particles have enough energy to fly off into the air as a gas. Boiling water turns into water vapor through evaporation, while freezing or staying the same would need less heat, not more.
3. Which is an example of condensation?
A) Ice cubes melting in a glass
B) A puddle drying in the sun
C) Water droplets forming on a cold can
D) Snow falling from clouds
Condensation is when a gas cools and turns back into a liquid. Water vapor in the warm air touches the cold can, loses heat, and becomes the tiny droplets you see on the outside.
4. Why does a gas fill its entire container?
A) Its particles are packed tightly
B) Its particles move fast and spread apart
C) Its particles do not move at all
D) Its particles are heavier than liquid
Gas particles move quickly and have very little holding them together, so they fly off in every direction. They keep spreading until they bump up against the walls, which is why a gas fills its whole container.
Part B: Fill in the Blank
Write the correct answer on each line.
1. The temperature at which ice melts into water is 0 degrees Celsius.
Water freezes and melts at the same temperature on the Celsius scale, and that point is set right where ice and liquid water meet. Ice melts into water at 0 degrees Celsius.
2. Adding heat to a substance makes its particles move faster.
Heat is energy of motion for particles, so adding heat means the particles get more energy. With more energy they vibrate, slide, or fly around faster than before.
3. When water vapor cools, it condenses back into liquid water.
When water vapor loses heat, its particles slow down and start sticking together into tiny drops. The word for a gas changing into a liquid this way is condenses.
4. A chocolate bar left in the sun will melt because heat changes its state.
Sunlight warms the chocolate enough that its particles can slip past each other instead of staying solid. The added heat makes the chocolate bar melt from a solid into a soft liquid.
5. The process of a liquid changing into a solid is called freezing.
When a liquid cools, its particles slow down until they lock into a fixed pattern. That cooling change from liquid to solid is called freezing.