Page 24 - ICSE Chemistry 8

4. The total mass of the ________________ is equal to the total mass of the ________________
in a chemical reac on.
5. On burning magnesium in air, ________________ is formed.

Terms to Know

Ma er: Anything that has mass and occupies space

Kine c molecular theory of ma er: A theory that states that ma er consists of very ny atoms/molecule
that are constantly in mo on and possess kine c energy

Intermolecular force of a rac on: Force of a rac on that exist between molecules of states of ma er
Intermolecular space: Distance between molecules of states of ma er

Quick Review

• Ma er is anything that has mass and occupies space.
• Solid, liquid and gas are the three states of ma er.

• Solids have fi xed shape and volume.
• Liquids have fi xed volume and they take the shape of the container in which they are poured.

• Gases have no fi xed shape or volume. They take the shape of the container they are kept in.
• The kine c molecular theory of ma er states that ma er consists of very ny molecules that are
constantly in mo on and possess kine c energy.
• There exists intermolecular force of a rac on between the molecules and the distance between the
molecules is called intermolecular space.
• The state of ma er is decided on the basis of intermolecular force of a rac on and intermolecular
spaces between the par cles of ma er.
• The kine c molecular theory explains the behaviour of ma er in diff erent states.

• The law of conserva on of mass states that mass can neither be created nor destroyed.
• The density of the ma er and the volume occupied by the ma er may vary within a system but the
mass remains constant.

• The law of conserva on of mass holds because naturally occurring elements are stable.
• The substances may show change in size, shape, kine c energy and other proper es during a physical
change but the total mass remains the same.
• The total mass during a chemical reac on or a chemical change remains the same. We can say that the
total mass of the reactants is equal to the total mass of the products in a chemical reac on.

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