What do these two changes have in common?
rust forming on a bicycle frame
newly poured concrete becoming hard
Both are only physical changes. Both are caused by cooling. Both are caused by heating. Both are chemical changes.
Step 1: Think about each change.
Rust forming on a bicycle frame is a chemical change. Oxygen in the air reacts with iron in the bicycle frame. The outside of the frame turns into a different type of matter called rust. Rust is reddish-brown and falls apart easily.
Concrete hardening is a chemical change. The chemicals in the concrete react with each other to form a different type of matter. The new matter is hard and strong.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.