Matter In Our Surroundings – Inter Conversion of States of Matter
* Inter conversion of states is the phenomenon of the change of matter from one state to another and back to original state, by altering the temperature.
* The process where a solid changes to a liquid is called melting.
* Latent heat of fusion is the amount of heat energy required to change 1 kilograms of a solid into liquid.
* The process where a liquid changes to gas as its boiling point is called vaporisation.
* Latent heat of vaporisation is the amount of heat required to change a unit mass of liquid to gas at atmospheric pressure.
* Evaporation is the process where a liquid changes into vapour at any temperature below its boiling point.
The factors effecting evaporation are:
* Surface area
* Temperature
* Wind speed
* The process where vapour changes onto a liquid is called condensation.
* The process where a liquid changes into a solid is freezing.
* Sublimation is the process where a solid, on heating, directly changes into gas without changing into liquid, and gas on cooling directly changes to solid without changing into liquid.
* Applying pressure and reducing temperature can liquefy gases.
Specific Heat Capacity
* The quantity of heat absorbed or emitted, “ΔQ”, by a body is directly proportional to its mass and change in temperature, “ΔT”.
* Heat capacity ‘S’ of a body is defined as the heat absorbed or emitted per unit change in its temperature.
* The SI unit of heat capacity is J/K.
* Specific heat capacity ‘S’ is the quantity of heat absorbed or emitted by a unit mass of a substance for a change in its temperature of one unit.
* The SI unit of specific heat capacity is J/Kg K.
* When a given substance is expresses in “moles”, its specific heat capacity is known as molar specific heat capacity ‘c’.
* The SI unit of molar specific heat capacity is J/mol K.
Calorimetry
* Calorimetry is the science of measuring heat.
* Principal of Calorimetry: when two or more bodies at different temperatures are brought into thermal contact, and if no heat is allowed to escape to the surroundings, then the total heat lost by the hot bodies must be equal to the total heat gained by the cold bodies.
* The amount of heat lost or gained by the body is expresses by the equation:
Δ = msΔT
Change of State
* Transition of matter from one state to another is called change of state.
* The change of state from solid to liquid is called melting.
* The change of state from solid to liquid is called fusion.
* The change of state from liquid to gaseous state is called boiling or vaporisation.
* The change of state from solid to liquid is called Condensation.
* The temperature at which the solid and liquid states of substance are the thermal equilibrium with each other is called the melting point.
* The amount of heat absorbed by a unit mass of substance to convert it completely from one state to another state is called latent heat (L).
* The latent heat absorbed in the case of solid-to-liquid transition is called latent heat of fusion (Lf).
* The constant temperature at which the liquid and the vapour states of the substance co-exist is called boiling point.
* The heat requires to covert one unit mass of a substance completely from the liquid to gaseous state is called latent heat of vaporisation (Lv).
Convection and Radiation
* Heat transfer by actual motion of matter from one region to another is known as thermal convection.
* Convectional is possible only in fluids.
* Thermal convection can be either natural of forced.
* The steady surface winds blowing from the north- east and the south- east, towards the equator are called the trade winds.
* The electromagnetic waves emitted by a body by virtue of its temperature is called is called thermal radiation.
* Heat energy received from the sun is in the form of radiation.
* Heat is transmitted through vacuum in the form of electromagnetic waves.
* Black bodies have a greater capacity of absorbing radiant energy.
* Heat is an invisible form of energy that causes the sensation of hotness or coldness.
* Heat energy can be defined as the sum of the potential energy and kinetic energy of all the molecules of a substance. The total amount of heat energy is called enthalpy.
* Heat energy always flows from a body at higher temperature to a body at lower temperature, till their temperatures are equal, which called equilibrium temperature.
* The branch of physics that deals with the measurement of heat energy is called colorimetry.
* The SI unit for heat is joule.
Specific Heat
* The amount of heat energy supplied to a substance directly proportional to the change in its temperature.
* The amount of heat energy required to increase the temperature of a given mass of substance by 1°C is called its heat capacity (C).C = Q/Δt
* The SI unit of heat capacity is Jk-1
* Specific heat capacity is defined as the amount of heat energy required per unit mass of a substance to change its temperature by one unit
Specific heat capacity, s = 1/m(Q Δt)
* The SI unit of specific heat capacity is J kg-1 K-1
* The specific heat capacity of water is cal g-1°C-1, which is equal to 4200 Jkg-1 K-1