What do these two changes have in common?
an antacid tablet reacting with water
a penny tarnishing
A: Both are caused by cooling.
B: Both are caused by heating.
C: Both are only physical changes.
D: Both are chemical changes.
Step 1: Think about each change.
An antacid tablet reacting with water is a chemical change. When the tablet touches water, the type of matter in the tablet changes and carbon dioxide gas is released. This gas makes the water fizz.
Metal turning less shiny over time is called tarnishing. A penny tarnishing is a chemical change. When air touches the penny, the surface of the penny changes into a different type of matter. This matter makes the penny dull.
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.