What do these two changes have in common?
roasting a marshmallow over a campfire
a copper statue turning green
Both are caused by heating. Both are caused by cooling. Both are only physical changes. Both are chemical changes.
Chemical changes and physical changes are two common ways matter can change.
In a chemical change, the type of matter changes. The types of matter before and after a chemical change are always different.
Some chemical changes are caused by heating or cooling. For example, burning a piece of paper is a chemical change caused by heating. When paper gets hot enough, it re­acts with oxygen in the air and burns. The paper and oxygen change into ash and smoke.
In a physical change, the type of matter stays the same. The types of matter before and after a physical change are always the same.
A change of state is a type of physical change. Changes of state can be caused by heating or cooling. For example, ice melting is a physical change that can be caused by heating. Ice and liquid water are made of the same type of matter: water.
The law of conservation of mass says that all physical and chemical changes conserve mass. Conserve means to keep the same. So, the total mass before a physical or chemical change is equal to the total mass after the change.
Step 1: Think about each change.
Roasting a marshmallow is a chemical change. The type of matter on the outside of the marshmallow changes. As a marshmallow is roasted, it turns brown and crispy.
A copper statue turning green is a chemical change. The copper reacts with oxygen in the air. This reaction forms a different type of matter called copper oxide. The copper oxide is green.
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.
Roasting is caused by heating. But a copper statue turning green is not.
Both are caused by cooling.
Neither change is caused by cooling.