What is the difference between matter and substance?

Substance is a sample of matter.

It's easy to see why you'd have trouble with the two words.

• Matter can be identified by its characteristic inertial and gravitational mass and the space that it occupies. On earth matter is commonly found in three different states: solid, liquid, and gas.
• Substance is a sample of matter whose physical and chemical properties are the same throughout the sample because the matter has a constant composition. It is common to see substances changing from one state of matter to another.

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