Properties of Matter — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Particles in a solid move quickly and spread far apart from each other.
Corrected: Particles in a solid vibrate in place and are packed closely together.
In a solid, particles are held tightly together and only vibrate in place. Fast-moving, spread-out particles describe a gas, not a solid.
2. Fix the sentence:
A gas has a fixed shape and a fixed volume just like a solid does.
Corrected: A gas has no fixed shape and no fixed volume because its particles spread out to fill any container.
Unlike a solid, a gas has neither a fixed shape nor a fixed volume because its particles move freely and spread out to fill whatever container they are in.
3. Fix the sentence:
When water evaporates, the water molecules are destroyed and disappear forever.
Corrected: When water evaporates, the water molecules change from liquid to gas but are not destroyed. They move into the air.
Evaporation is a change of state, not a destruction of matter. The water molecules still exist; they simply gain enough energy to leave the liquid surface and enter the air as water vapor.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A liquid has a fixed volume but takes the shape of its container.
A liquid's particles slide past each other, so the liquid flows and takes the shape of whatever container holds it, even though the total volume stays the same.
2. The change from a solid directly to a gas without becoming a liquid is called sublimation.
Sublimation skips the liquid stage entirely. A common example is dry ice turning directly into carbon dioxide gas without ever melting into a liquid.
3. Adding thermal energy to a solid can cause it to melt and become a liquid.
When enough thermal energy is added, the particles in a solid vibrate fast enough to break free of their fixed positions, causing the solid to melt into a liquid.
4. When a gas loses energy and changes to a liquid, the process is called condensation.
Condensation happens when gas particles lose enough energy to slow down and come together as a liquid, like water droplets forming on a cold window.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Compare how particles move in a liquid versus a gas.
Sample answer: In a liquid, particles slide past each other and stay close together but can change positions. In a gas, particles move very fast in all directions and spread far apart to fill the entire container.
A good answer includes: In a liquid, particles slide past each other and stay close together but can change positions. In a gas, particles move very fast in all directions and spread far apart to fill the entire container.
2. Why does a puddle of water disappear on a warm sunny day even though nobody heated it on a stove?
Sample answer: The sun provides thermal energy to the water molecules in the puddle. Some molecules at the surface gain enough energy to escape into the air as water vapor, which is the process of evaporation.
A good answer includes: The sun provides thermal energy to the water molecules in the puddle. Some molecules at the surface gain enough energy to escape into the air as water vapor, which is the process of evaporation.