What do these two changes have in common?
a piece of apple turning brown
compost rotting
Both are chemical changes. Both are caused by cooling. Both are caused by heating. Both are only physical 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.
A piece of apple turning brown is a chemical change. The apple reacts with oxygen in the air and turns into a different type of matter.
If you scrape off the brown layer of the apple, the inside is still white. The inside hasn't touched the air. So the chemical change didn't happen to that part of the apple.
Compost forms from the remains of plants and animals, such as vegetable scraps and egg shells. Compost rotting is a chemical change. As the compost rots, it breaks down and turns into a different type of matter.
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.