Matter in our surroundings can be broken down to 5 sub-topics, namely Matter, States of Matter, Change of States of Matter, Evaporation and Plasma and Bose-Einstein condensate. We take up each topic one by one.
Topic 1: Matter
1. Physical Nature of Matter
(i) Matter is anything which occupies space and has mass.
(ii) Matter is made up of particles (atoms or molecules).
2. Characteristics properties of the particles of Matter
(i) Particles of matter are so small to be seen with naked eyes. Notice that a crystal of copper sulphate gives colour even on repeated dilutions.
(ii) Matter is constituted by a large number of particles.
(iii) Particles of matter have spaces between them. Eg. Sugar/ salt dissolve in water without raising the volume of water because sugar/salt go into the spaces between the water molecules.
(iv) Particles of matter are continuously moving. Eg. We can get the odour of the perfume/agarbatti sprayed in one corner to the other corner of the room due to the kinetic energy possessed by the particles.
(iv)Particles of matter attract each other. Due to forces of attraction between the particles we have different states of matter.
Topic 2: States of Matter
1. States of Matter
(i) Matter around us exists in three states – (i) Solid; (ii) Liquid and (iii) Gas.
(ii) These three states differ from one another due to the difference in (a) pacing; (b) Interparticle distance; (c) interparticle forces of attraction; (d) Shape and Volume; (e) Compressibility; (f) Rigidity/Fluidity; (g) Energy; (h) Density; and (i ) Diffusion.
(iii)On the account of the above differences – Solids, Liquids and Gases differ in the following respects:-
(a) Packing is the manner in which the atoms or molecules are arranged in inside the solid.
(b) Inter-particle distance means the distance between two particles. If the interparticle distance is small the matter is less compressible.
(c) Interparticle forces of attraction when high indicates that the matter is in solid form.
(d) Shape and Volume are a general indication of the state of matter.
(e) Compressibility is the tendency to decrease volume when some outside force is applied.
(f) Rigidity is the tendency to maintain shape when some outside force is applied.
(g) Fluidity is the tendency to flow.
(h) Kinetic energy is the energy possessed by particles due to motion.
(i) Density is mass per unit volume.
(j) Diffusion is the intermixing of the particles of different states of matter on their own.
Topic 3: Change of State of Matter
We know matter can exist in three different states, which are Solid, Liquid and Gas.
1. The states of matter are inter-convertible. Interconvertible nature means Solids gets converted to Liquid and Liquid can be converted to Gas.
2. Change of State –Change of State( conversion of Solid to Liquid to Gas) happens due to these two factors:
(a)Change in Temperature
(b)Change in Pressure.
3. Temperature and Heat Definitions to understand change of State
(i) Melting point is the temperature at which a solid melt to become a liquid at atmospheric (in short it is written as atm) pressure. The process of melting (change of solid into liquid state) is also called Fusion. The melting point of ice is 0ºC (C for Celsius) or 273.16 K (K for Kelvin).
(ii) Boiling point is the temperature at which a liquid starts boiling at the atmospheric pressure (1 atm). The boiling point of water is 100ºC (C for Celsius) or 373.16 k (K for Kelvin).
(iii) Sublimation is the direct conversion of a solid into the gaseous state on heating and vice-versa without going into the liquid state. For eg. Camphor, Naphthalene are solids which undergo sublimation to become Gases directly without changing state to Liquid.
(iv) Vapourisation/Vaporization is the process of conversion of Liquid to Gaseous state at a specific condition of temperature and pressure.
(v) Freezing point is the temperature at which a liquid freezes to become a solid at atmospheric pressure. The process of freezing (change of liquid into solid state) is also called Solidification.
(vi) Condensation is the process of changing a gas / vapour to a liquid by cooling. It is the opposite of vapourisaton.
(vii) Latent Heat is the heat energy which has to be supplied to change the state of substance. Latent Heat means Hidden heat. Latent heat does not increase the temperature.
(viii) Latent heat of Fusion (Solid changes to Liquid) is the amount of heat required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point.
(ix) Latent heat of Vaporisation (Liquid changes to Gas) is the amount of heat required to change 1 kg of a liquid into vapours at atmospheric pressure at its boiling point.
4. Temperature Scale
(i) There is a difference between Heat and Temperature. Heat is the amount of energy in a body and is measured in Joules. Temperature is degree of hotness or coldness of a body. It is measured in Fahrenheit or Celsius or Kelvin.
(ii) Historically there are three scales for measuring temperature. First is Fahrenheit scale. Then came the Celsius Scale. Finally, the SI unit of temperature is Kelvin. All the three scales are interconvertible.
(iii) Temperature in Kelvin Scale = Temperature in Celsius Scale + 273 [ 0ºC = 273 K]
(iv) Temperature in Celsius Scale = Temperature in Kelvin Scale – 273
(v) Temperature in Fahrenheit Scale °F = (temperature in Celsius) + 32
5. Effect of Change in Temperature
(i) When a solid is heated, the kinetic energy of its particles increases. Due to increase in kinetic energy, the particles start vibrating. The energy supplied by the heat overcomes the forces of attraction between the particles.
(ii) When a certain temperature is reached, the particles have enough energy to break the force of attraction between each other. As the force of attraction breaks, the solid becomes a liquid at this particular temperature called melting point. Similarly, if the liquid is heated again, then at a particular temperature, it gets converted to gas.
(iii) The reverse process can also take place. When heat is taken from a gas, it can get converted into a liquid. When heat is taken from a liquid it gets converted into a solid.
6. Effect of change in Pressure
(i) The physical state of a substance can be changed by changing the pressure.
(ii) An increase in pressure brings the particles closer and increases the force of attraction between them, which in turn changes its state. For example, when high pressure is applied to a gas and its temperature is reduced, the gas gets converted to a liquid. Or we say the gas has been liquefied.
(iii) Pressure is measured in atmosphere(atm) unit. The weight of a column of air in the atmosphere at sea level is termed as 1 atmospheric pressure (1 atm). As we move to a mountain, the higher we go, the column of air decreases and therefore pressure decreases. Pressure is higher at sea level as compared to on a hilly mountain.
(iv) 1 atm = 1.01 × 105 Pa [Pa = Pascal, SI unit of pressure]
Topic 4: Evaporation
(i) The phenomenon of change of a liquid into its vapours at any temperature below its boiling point is known as evaporation. It is a surface phenomenon. It is a continuous or ongoing process which occurs at a much slower rate.
(ii) Factors affecting evaporation:
(a) Surface Area: When the surface area increases the rate of evaporation increases. When we spread the cloths to dry, it dries up faster.
(b) Temperature: As the temperature increases the rate of evaporation increases. This is due to the fact that the surface molecules of the liquid get sufficient kinetic energy and leave the liquid.
(c) Humidity: As the humidity increases the rate of evaporation decreases. The amount of water vapour present in the air at a particular temperature is called Humidity. As the air can hold a certain amount of water vapour at a particular temperature, so when this capacity becomes full, air can hold no more water vapour and no evaporation occurs. In a humid day, we sweat a lot because the capacity of air to hold water vapour is full and therefore, the sweat which comes out does not evaporate. The process of evaporation of water from aerial parts of plants especially leaves is known as transpiration.
(d)Wind Speed: Evaporation increases with an increase in the wind speed and vice-versa.
(iii) Evaporation causes cooling because some of the particles on the surface of the liquid which have high kinetic energy overcome the forces of attraction by the neighbouring particles, leave the liquid surface and get converted into vapours. So, the remaining particles have less average kinetic energy, hence the temperature decreases.
(iv) Examples of evaporation causing cooling in daily life:
(a) When the hot tea is poured into a saucer, it is exposed to a large area and causes evaporation. As evaporation causes cooling, the tea becomes cool.
(b) In the summer season, the water gets cool in an earthen pot. This is because earthen pot has fine pores in it through which water seeps out. When this water evaporates, it gets cooler and the water inside gets cooler.
(c) When we sweat, we sit under a fan to feel cool. When the sweat evaporates under the fan, it causes cooling and we feel cool.
(d) Doctors advise patients with fever to keep a wet cloth on their forehead. As the water evaporates when in contact with the hot forehead, it causes cooling and the temperature of the person comes down.
Topic 5: Plasma and Bose-Einstein Condensate
1. Plasma and Bose-Einstein Condensate [two new States of matter]
(i) Plasma – It is the fourth state of matter consisting of super-energetic particles in the form of ionised gases. The fluorescent tube, neon sign bulbs consist of plasma. The plasma is created in stars due to high temperature.
(ii) Bose-Einstein Condensate (B.E.C) – It is the fifth state of matter which is formed from matter that has been cooled to near absolute zero (-273°C) thus the velocities of atoms decreases causing individual atoms to overlap forming a single super atom. For eg: – a rotating B.E.C could be used as a model black hole, allowing light to enter but not to escape.