What do these two changes have in common?
rust forming on a metal gate
burning food on a stove
Both are caused by heating. Both are only physical changes. Both are caused by cooling. 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.
Rust forming on a metal gate is a chemical change. As the gate rusts, the metal turns into a different type of matter called rust. Rust is reddish-brown and falls apart easily.
Burning food on a stove is a chemical change. When the food burns, the type of matter in it changes. The food turns black and gives off smoke.
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.
Burning is caused by heating. But rust forming on a metal gate is not.
Both are caused by cooling.
Neither change is caused by cooling.