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Substances that can flow are called fluids. Both gases and liquids are fluids, e.g. gases (carbon dioxide, hydrogen), liquids (water, petrol and sulphuric acid).

a. False

b. False

c. True

d. True

e. False

Mass is the quantity of matter contained in the body.

The particles in a substance are not at rest (in motion),and they move randomly in all possible directions in a zig-zag Path

Molecles are made of atoms. molecules exhibit the properties of that kind of matter and has independent existance.

Weight of body on moon = 1/6 th of its weight on earth

∴ Body will weigh 1/6 x 6 = 1 kg on moon

The molecules can move only when there are gaps or space between them, this space is called intermodular space.

(a) The molecules of matter are always in motion and attract each other with a force called intermodular force of attraction due to which  they are held together .

(b) The molecules can move only when there are gaps or space between them, this space is called intermolecular space.

Mass of a body does not change with change in gravity. So mass of a body will remain the same on moon.

The molecules of matter are always in motion and attract each other with a force, and this force is called intermodular force of attraction due to which they are held together.

Melting — The change from the solid state to the liquid state by heating at a fixed temperature is called melting.

Melting Point — It can be defined as the fixed temperature at which a solid start changing to its liquid state.

MELTING POINT OF SOLID (WAX): Put some wax in a test tube. Insert a thermometer in solid wax, so that bulb of thermometer remains in wax and does not touch the sides. Clamp the test tube along with a thermometer in hot bath i.e. in water contained in the beaker and set up the apparatus as shown. Note the temperature Heat the beaker over the flame of burner and record the temperature after every minute. First temperature rises and then reaches 55 °C and wax shines in the test tube. Temperature remains constant for nearly 5 minutes i.e. at 55 °C. This means Wax is melting and temperature remains constant till the whole of wax is melted. Then temperature rises again every minute till it reaches 

Conclusion: The temperature remains constant at 55°C while changing from solid to liquid. This means 55°C is the melting point and heat is absorbed without a change in temperature. This heat is absorbed at constant temperature till whole of wax is melted.

(a) is Boiling point

(b) is Evaporation.

The process involved in two cases is vaporization or boiling.

(a) MELTING POINT OF ICE: “Is the constant temperature at which it starts (melting) changing from ice to water.” It is 0°C for ice. 

(b) BOILING POINT OF WATER: “Is that constant temperature at which water starts (BOILING) changing from water to steam (vapors)”. It is 100°C for water.

Natural matter: Wood, silk, coal, water, fruits. 

Man made matter: Plastic, medicines, detergents, ceramic, cotton, glass, nylon.

Wires cannot be drawn from materials such as stone or wood, is because these materials are non – conductors of electricity.

VAPORIZATION: “Change of liquid to vapors (gas) on heating at constant temperature is called VAPORIZATION.” When we heat a liquid temperature starts rising till it starts changing into vapors and then temperature remains constant for some time, until we are supplying heat. This heat supplied is being used to change every molecule of liquid into vapors and temperature does not rise until the whole of liquid is changed into vapors. 

BOILING POINT: “The temperature at which a liquid starts changing into vapors or gas at constant temperature is called its BOILING POINT.”

(a) Camphor, iodine, naphthalene, ammonium chloride, dry ice (solid carbon dioxide), etc.

(b) Gases do not change their state on heating.

Example: O₂.

Matter can change from solid to liquid to gaseous state and back to solid state. This is called change of state of matter. 

(a) Melting— The process of conversion of a solid into liquid on heating. e.g. Ice to water.

(b) Vaporization— The process of conversion of a liquid into vapour on heating. e.g. Water to water vapour. 

(c) Condensation— The process of conversion of vapour into a liquid. e.g. Water vapour to water. 

(d) Freezing— The process of conversion of a liquid into a solid. e.g. Water to ice. 

(e) Melting point— The constant temperature at which a solid melts into a liquid. M.P. of ice – 0°C. 

(f) Boiling point— The constant temperature at which a liquid starts boiling. B.P. of water – 100°C.

(a) The change of a solid into a liquid is called melting or fusion.

(b) The process in which a solid directly changes into a gas is called sublimation.

(c) The change of water vapour into water is called condensation.

(d) The temperature at which a liquid starts changing into its vapor state is evaporation or vaporisation.

The process by which a solid changes into a liquid is called

(b) melting

The process by which a solid change into a liquid is called melting.

surface of liquid

False Evaporation takes place over the entire mass of the liquid.

As a liquid is heated, its particles starts gaining energy and move more vigorously which increases the gaps between the particles and decreasing the force of attraction. Ultimately a liquid changes into gaseous state.

During interconversion of state of matter composition of substance remains the same matter changes from one state to another and back to the original state, while chemical reaction involves re-arrangement of the molecular structure and composition changes.

If some spirit is poured on cotton wrapped around the bulb of a thermometer, the reading of the thermometer falls. This shows that cooling is produced when a liquid evaporates taking heat from surroundings.

Water from oceans, rivers, lakes from leaves of trees (transpiration) changes into vapours when temperature increases or evaporates and enters the atomsphere as clouds when temperature falls the vapours change into water and some of it in the form of snow fall on mountains and earth in the form of water and hales and this continues. Thus water cycle is example of interconvertion of states of water.

False The ice melts at 0° by absorption of heat.

From the table given above, we note that as thermometer shows 100°C, it becomes constant and through heat is being supplied. This means boiling point of water is 100°C and the heat supplied is being used to convert every molecule of water into vapors (steam) till the whole of the water gets boiled off.

The state of matter which has no definite shape or volume is called

3. gas

Molecules of a liquid are held by weak intermolecular förces. This force is sirong enough to hold the molecules together but not strong enough to hold them at fixed positions. As a result liquids have a fixed volume but not shape.

(a) Solids have very closely packed atoms with minimum spaces between them while gases have atoms which are for apart with maximum spaces between them. Solids have a definite shape and are highly rigid while gases have no definite shape and are least rigid. 

(b) Sugar is soluble in water whereas talcum powder is not. 

(c) Every pure substance has a fired melting point or boiling point. 

(d) A bottle of perfume on opening evolves an odour because gases diffuse very easily and odour spreads over a large distance.