BASANT’S SCIENCE
PH-9777702608/9090455486
CLASS-iX
CHAPTE-Matter in our Surroundings
DIFFERENT TYPES OF TEMPERATURE
SCALES
James Prescott Joule
1.
There are four different scales used these days.
Celsius or centigrade scale. In this scale, L.F.P.(ice point)
is
taken to be zero and U.F.P. (steam point) is taken to be 100°C. The scale between U F P. and
L.F.P. is divided into 100 divisions all of equal size.
Reumer scale. In this scale, L.F.P. is 0°R and U.F.P. is 80°R. The scale is divided into 80
divisions all of equal size.
3. Fahrenheit scale. In this scale, L.F.P. is 32°F and U.F.P. is 212°F. The distance between
these two points is divided into 180 divisions.
4. Kelvin scale of temperature. In this scale, L.F.P. is 273 K and U.F.P. is 373 K. Its
divisions are of the same size as those of Celsius scale.
Whereas Celsius scale is used in most of the countries and is more
convenient than Reumer and fahrenheit scales, Kelvin scale is very widely used for
scientific work.
2.
Relation between Different Scales. If temperature of a body measured on different scales are C on Celsius; R
on Reumer; F on Fahrenheit; K on Kelvin and X on any other scale, then the relation between them is
EX: Temperature of a man on Fahrenheit scale is 98.6°F, what will it be on (i) Celsius scale; (ii) Kelvin scale ?
Ex: Change the following thermometer readings. - 273°C, -100°C, - 40°C, 30°C, 2,000°C to Kelvin scale.
-273°C = (-273 + 273) K = OK
BASANT’S SCIENCE
PH-9777702608/9090455486
CLASS-iX
CHAPTE-Matter in our Surroundings
- 100°C = (-100 + 273) K = 173 K
-40°C = (-40 + 273) K = 233K
30°C = (30 + 273) K = 303 K
2,000°C = (2,000 +273) K = 2,273 K
CAN MATTER CHANGE ITS STATE?
State of a matter change from solid to liquid to gas when it is heated.
In solids, particles are extremely close to each other due to strong intermolecular forces. When heat is
given to such a solid, kinetic energy of the particles slowly increases, resulting in strong vibrations of the
particles. When the total kinetic energy of the particles becomes more than the lattice energy, strong
vibrations compel them to leave their fixed positions. At this stage solid starts melting and the resultant
liquid takes shape of the container. The volume of the resultant liquid becomes generally larger than
that of the solid. When further heat is supplied, the kinetic energy of the particles further increases. The
distance between particles also increases. At some temperature, the distance between particles becomes
so much that these are free to move in a random motion throughout the container. This is called
gaseous state.
When ice at -10°C is slowly heated, temperature of ice gradually increases till at 0°C, the
temperature of the system remains constant when the ice changes into water and then
further rises. Explanation
At 0cC, when the ice melts, the temperature of the system does not change though the heat is
continuously supplied. The given heat is used up in overcoming the force of intermolecular attraction.
This results in the conversion of ice into water. As this heat energy is absorbed by ice without any rise in
temperature of the system, this heat is considered as hidden in the system and is known as latent heat.
Relation between boiling point of a liquid and the inter molecular forces of attraction
between the particles of a liquid.
Stronger the intermolecular forces of attraction, higher would be the boiling point. For example, particles
of alcohol have weaker intermolecular forces of attraction than those of water particles. This is in
conformity with the fact that alcohol boils at lower temperature of 78°C as compared to boiling point of
water which is 100°C.
Ice at 273K is less energetic than water at the same temperature.
Water at 273K is formed from ice at 273K by absorbing latent heat of fusion. Therefore energy content of
water at 273K is always higher than ice at 273K.
SPECIFIC LATENT HEAT OF FUSION
The specific latent heat of melting of substance is the quantity of heat required to convert 1
g of that substance from the solid to the liquid state without the change in its temperature.
Specific latent heat of melting and specific latent heat of fusion for a substance is the same
thing.
SPECIFIC LATENT HEAT OF VAPORISATION
The specific latent heat of vaporisation of substance is the
quantity of heat required to convert 1 g of that substance
from the liquid to the vapour state without the change in its
temperature.
The S.I. unit of specific it heat is joule per kilogramme (symbol J kg-1).
Other commonly used units are calorie per gram (symbol cal g-1) and kilo-calorie per kilogram (kcal
kg-1).
They are related as: 1 kcal kg-1 = 1 cal g-1 and 1 cal g -1 = 4.2 J g -1
Specific latent heat of fusion of ice: The specific latent heat of melting of ice is 80 cal g-1. This means
that 1g of ice at 0°C absorbs 80 cal of heat to convert o water at 0°C. Similarly, 1 g of water at
0°C gives out 80 cal of heat to convert into ice at 0°C. Hence, specific latent heat of fusion of ice is 80
cal g-1.
BASANT’S SCIENCE
PH-9777702608/9090455486
CLASS-iX
CHAPTE-Matter in our Surroundings