LATENT HEAT
1.The amount of heat gained or lost by unit mass of a subastance at a constant temperature is called
specific latent heat or heat of formation(L)
2.Specific latent heat or latent heat depends on nature and state of substance.
3.Units of latent heat:Calgm-1, Jkg-1
Dimensions:M0L2T-1
4.The quantity of heat taken or given out by unit mass of a substance when it changes from solid to liquid state or liquid to solid state at constant temperature is known as latent heat of fusion
5.Latent heat of fusion of ice =80calgm-1 or \(
3.36 \times 10^5 Jkg^{ - 1}
\)
6.The quantity of heat taken or given out by unit mass of substance when it changes from liquid to vapour state or from vapour state to liquid state at constant temperature is known as latent heat of vapourisation
7.Latent heat of vapourisation of water or Latent heat of steam =540 Calgm-1 or \(
2.26 \times 10^6 Jkg^{ - 1}
\)
8.The conversion of sold directly into vapour is called sublimation.e.g. camphor,napthalene balls ,iodine.
The amount of heat required to change the unit mass of solid directly into vapour at a given tempearture is called heat of sublimation.
9.latent heat of vapourisation of water decreases with the increase of pressure.It is maximum atand decreases with increase of boiling point(L=600-0.6\(\theta\))in Calgm-1
10.The temperature at which a liquid converts to a solid is called its freezing point.
11.The temperature at which a liquid converts to vapour is called its boiling point
12.Certain substances expand while changing from liquid to solid state .e.g:water,castiron,bismutg and type metal
13.Most of the substances expand on liquification.e.g:silver,copper,gold
14.Impurities generally lower the melting point(e.g:ethylene glycol or alcohol acts as antifreezing agent)
15.Addition of impurities increases the boiling point of a liquid generally.
16.The cooling of a liquid below its freezing point is called super cooling(e.g water can be cooled upto -120c)
17.The heating of a liquid above its freezing point is called super heating(e.g water can be super heated upto 1370c)
18.Super heated or super cooled liquid is unstable
19.Melting of ice under pressure and its resolidification when pressure is released is called regelation
Skating and glacier motion are due to regelation
20.During tha change of state ,heat gained or lost by the substance is Q=mL
21.Solutions have a lower freezing point than that of the pure solvent
23.For subliming solids,the boling point will be less than the melting point
24.Sea water boils at a temperature greater than 1000c .Dissolves impurities increase the boling point
25.In a pressure cooker water boils at a temperature above
26.When 1ml of water is boiled,about 1671CC of steam is produced
27.Cooking of rice in a pressure cooker is a quick process as water boils at a temperature above 1000c due to the increase in pressure
28.Latent heat of vapourisation of water is maximum at_00c and decreases with increase of temperature
29.Water absorbs or given outmore heat than any other substance for the same change in temperature as its specific heat is high
30.Water cannot be convertes into ice by adding ice to it.
31.Water cannot be boiled by sending steam into it.
32.Steam causes more severe burns than water at 1000c (steam has more heat i.e. latent heat which is given out on condensation)
33.In extinguishing fire hot water is preferred than cold water as hot water readily converts into steam which engulfs the fire and cuts off supply of oxygen
34.Ice at produces more cooling than water at 00c .