ICSE Class 9 Chemistry Chapter 01 Matter and its Composition

Matter and its Composition: Law of Conservation of Mass

Scope of Syllabus

Explanation of change of state of matter on the basis of Kinetic Theory of Matter. Main postulates of Kinetic Theory of Matter and explanation of change of state on the basis of Inter-particle space and Inter-particle attraction and collision.

Law of Conservation of Mass. Statement and explanation with examples.

Important Points to Remember

1. Anything that has weight and occupies space is called matter.

2. Matter has been classified into two types.

Matter is divided into two categories: Homogeneous and Heterogeneous.

3. The matter which has the same composition and same property in its every part is called homogeneous matter. Examples - salt solution, sugar solution.

4. The matter which has different compositions and different properties in its every part is called heterogeneous matter. Examples - polluted air, soil, etc.

5. The older belief is that all matter is composed of four basic elements, i.e., air, water, fire and earth.

6. John Dalton proposed the atomic theory. The postulates of Dalton's Atomic Theory are given below:

(i) All matter is composed of tiny invisible particles called atoms.

(ii) Atoms can neither be created nor be destroyed.

(iii) Atoms of same element have same size, shape and weight.

(iv) Atoms of different elements have different size, shape and weight.

(v) Atoms combine in small whole number ratio to form compound atoms.

(vi) Atom is the smallest unit of matter which takes part in a chemical reaction.

Three States of Matter and Kinetic Theory

7. The three different states of matter are (i) Solid (ii) Liquid (iii) Gas.

8. The difference between the three states of matter was found on the basis of their molecular motion which can be explained by kinetic theory of matter.

The main postulates of kinetic theory of matter are as follows:

(i) All particles are composed of tiny particles called atoms or molecules.

(ii) These molecules are in a state of unending motion, i.e., they possess kinetic energy.

(iii) The kinetic energy of molecules increases on supplying heat energy, i.e., the molecules start moving at a faster rate.

(iv) If the matter is cooled, then the kinetic energy of molecules decreases, i.e., the molecules slow down.

(v) As the intermolecular space increases, the intermolecular force of attraction decreases and if the intermolecular space decreases, the intermolecular force of attraction increases.

(vi) The force of attraction between the molecules is called as cohesive force if the particles are of same kind, and adhesive force if the particles are of different kinds.

Properties of Solids

9. Properties of solids:

(i) In solids, the molecules are closely or tightly packed.

(ii) The intermolecular space is minimum or negligible.

(iii) The intermolecular force of attraction is maximum.

(iv) They have definite shape and definite volume.

(v) They are generally rigid except some like rubber which changes its shape on applying external force but it regains its original shape on removal of the external force.

(vi) Solids have maximum density.

(vii) Solids do not show any appreciable change in size when heated or cooled.

(viii) Solids possess any (as the number of sides of solids) number of free surfaces.

(ix) When two solids kept in contact with each other, they do not intermix with each other, i.e., it does not undergo the process of diffusion.

(x) Solids do not flow.

10. Solids have definite shape and definite volume because in solids the intermolecular space is minimum or negligible but intermolecular force of attraction is maximum. Therefore, the molecules of solid cannot move, they can only vibrate, i.e., they possess minimum kinetic energy. So, they cannot move from one position to another.

Properties of Liquids

11. Properties of liquid:

(i) In liquids, the molecules are loosely packed.

(ii) The intermolecular space in liquids is more than solids but less than gases.

(iii) The intermolecular force of attraction in liquids is less than solids but more than gases.

(iv) They have definite volume but not definite shape. They only take the shape of the container.

(v) Liquids have less density as compared to solids.

(vi) Liquids flow from higher level to lower level.

(vii) When heated or cooled, the volume of liquid shows appreciable change, which is not seen in the case of solids.

(viii) Liquids have only one free surface.

(ix) The liquids when kept in contact with each other intermix with each other to form homogeneous solution. Mixture of miscible liquids like ethanol and water intermix thoroughly to form homogeneous solution whereas immiscible liquids like oil and water do not diffuse to form homogeneous solution.

12. In liquids, the intermolecular force of attraction is enough to keep the molecules in contact with each other. Hence, the molecules of liquids are free to move within the body of the liquid. Therefore they can easily take the shape of container.

Properties of Gases

13. Properties of gases:

(i) The molecules in gases are far apart from each other.

(ii) The intermolecular space is maximum.

(iii) The intermolecular force of attraction is minimum or negligible.

(iv) The gases have neither definite shape nor definite volume.

(v) Gases flow easily in all directions.

(vi) Gases have minimum density.

(vii) Gases have maximum compressibility. As the intermolecular space is maximum. So, on applying pressure, the molecules come closer to each other.

(viii) Gases do not have any free surface.

(ix) Gases rapidly undergo the process of diffusion. It is the process of intermixing of gases without applying any external agency so as to form homogeneous mixture.

(x) When heated or cooled gases show appreciable expansion or contraction.

14. The intermolecular space in gases is maximum, therefore the molecules do not feel the appreciable force of attraction. Moreover, the molecules have maximum kinetic energy. So the molecules move freely practically in all directions filling all the spaces. Thus, they have neither definite volume nor definite shape.

Interconversion of Matter

15. The phenomenon of the conversion of matter from its one state to another and back to its original state by changing the conditions like temperature and pressure etc. is called interconversion of matter.

16. The two factors which bring about the interconversion of matter are:

(i) Temperature

(ii) Pressure

17. Effect of temperature on the different states of matter.

Conversion of solid into liquid.

(a) The process of conversion of the solid into its liquid by absorbing heat is called as the process of melting or fusion.

(b) The constant temperature at which solid gets converted into liquid is called melting point. For example, melting point of ice is 0°C.

Ice - Water (solid) - (liquid)

Conversion of liquid into solid.

(a) The process of conversion of liquid into solid by giving out heat energy or by reducing temperature or by cooling is called freezing or solidification.

(b) The constant temperature at which liquid changes into solid is called freezing point.

(c) The numerical value of melting point and freezing point is same.

Water - Ice (liquid) - (solid)

Conversion of liquid into gaseous state or vapour state.

(a) The process of conversion of liquid into its vapour at a constant temperature is called as boiling or vaporisation.

(b) The process of conversion of liquid into its vapour at any temperature is called evaporation. The process of evaporation takes place much below boiling point.

(c) The constant temperature at which liquid gets converted into its vapour is called boiling point.

Water - Water vapour (liquid) - (vapour)

The differences between evaporation and boiling are:

Conversion of gaseous state or vapours into liquid.

The process by which gaseous state or vapour changes into liquid state on cooling is called condensation.

Water vapour - Water (vapour) - (liquid)

Direct conversion of solid into vapour state.

Certain solids on heating or without heating directly change into their vapour state without passing through the liquid state. This process is called the process of sublimation. For example, dry ice, naphthalene balls, iodine crystals, ammonium chloride.

NH3Cl - NH3 + HCl (cool)

The differences between gas and vapour are:

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