1) Physical change. A physical change affects the form of the substance, but the chemical composition remains the same. While in a chemical change, the composition of the substance changes. We can also say that in a chemical change a new substance is formed.
Freezing and boiling water, for instance, is a physical change. Ice is still water and vapor is still water. Water does not change in the process.
Dissolving. When we dissolve sugar in water, the sugar and the water remain the same. No new substances are formed.
Rusting. When a bar of iron rusts, a new substance is formed. This new substance is called iron oxide. Rusting is a chemical change.
How do we know a chemical change occurs?
There is a change in color, and odor or bubbles are formed.
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