Questions: Boiling and Condensation

Question 1

You see water droplets forming on the outside of a cold glass of lemonade on a warm day. Where did the water come from?

• A. The lemonade leaked through the glass
• B. The cold glass cooled the water vapor in the warm air, and it condensed into liquid droplets
• C. The ice inside the glass pushed water out through tiny holes
• D. The glass is sweating, just like a person does

Answer: (B)

The warm air around the glass contains invisible water vapor. When this vapor touches the cold surface of the glass, it loses heat and condenses — turns from gas back into liquid. The droplets come from the air, not from inside the glass.

Question 2

Boiling water keeps getting hotter the longer you heat it.

• T. True
• F. False

Answer: False

False. Once water reaches its boiling point (100 degrees Celsius at normal air pressure), its temperature stops rising. All the extra heat energy goes into turning the liquid water into gas (steam) rather than making the water hotter.

Question 3

What is condensation?

Model answer: Condensation is when a gas cools down and turns into a liquid. For example, water vapor in the air turns into liquid water droplets when it touches a cold surface.

Condensation is the reverse of boiling or evaporation. Gas particles slow down as they lose heat, come closer together, and form a liquid. You see condensation on bathroom mirrors after a hot shower and on cold windows on a warm, humid day.