You leave a chocolate bar on a sunny windowsill and it becomes soft and gooey. What happened?
AThe chocolate disappeared because of the heat
BThe chocolate melted — the heat from the sun changed it from solid to liquid
CThe chocolate became a gas because it got too hot
DThe sun broke the chocolate into smaller pieces
The heat from the sun raised the chocolate's temperature past its melting point, turning it from a solid into a soft, flowing liquid. The chocolate did not disappear or become a gas — it simply changed state from solid to liquid.
Question 2 True / False
Freezing and melting are reverse processes of each other.
TTrue
FFalse
Answer: True
True. Melting turns a solid into a liquid by adding heat. Freezing turns a liquid into a solid by removing heat. They are exact opposites. You can melt an ice cube into water and then freeze that water back into an ice cube — the matter goes back and forth between the two states.
Question 3 Short Answer
Why does an ice cube melt faster on a warm day than on a cold day?
Think about your answer, then reveal below.
Model answer: On a warm day, the surrounding air has more heat to transfer to the ice cube, so the ice gains heat faster and reaches its melting point more quickly.
Melting requires heat energy. The warmer the environment around the ice, the faster heat flows into the ice. On a cold day, there is less heat available in the air, so the ice gains heat slowly and melts slowly.