Wednesday, May 25, 2011

Gaseous State–Measurable Properties

The measurable properties of gases are:-
1. Mass  
2. Volume  
3. Temperature  
4. Pressure.
1.   MASS
The mass of gas can be determined by weighing the container in which the gas is enclosed and weighing the container again when vaccumised (empty).The difference between two weights will give the mass of the gas. From mass, the number of moles can be calculated using the relation
Number of moles = mass of gas in grams / gram molecules mass
Number of molecules  =  Number of moles ´ Avogadro’s Number (N)
The Volume of any substance is the space occupied by that substance. For gases, the volume of sample is the same as the volume of the container in which it is held. Generally, the volume is specified in units of Litre (L),  Milliliters (ml) , Cubic decimeter (dm3) .
\            1L =1dm3 =   1000ml
Temperature is a measure of the degree of hotness of a substance. The measurement of temperature is based upon the principle that substances expand on heating. The most common substances whose expansion is made in measurement of temperature is Mercury (Hg). There are three different scales on which temperature are measured. These are;
·                    Centigrade or Celsius scale
·                    Fahrenheit scale
·                    Kelvin scale
In Celsius scale, the freezing point of water is taken as 0°C and boiling of water as 100°C at normal atmosphere pressure & then dividing the space in range into 100 equal parts.
In Fahrenheit scale, the freezing point of water is taken as 32°F and the boiling point of water as 212°F and range is divided into 180 degrees.
*(C.T.M) Temperature in Celsius can be converted to Fahrenheit scale by following relation;
                            Fo  = 9/5 Co + 32          or   Co  =   5/9 Fo 32
The Kelvin scale of temperature takes the lowest temperature of –273.15° as 0k. It is a better scale than Celsius scale because it does not involve negative values. The two scales are related by following relation.  
K  = Co + 273  
Pressure is force per unit area. A gas exerts uniform pressure in all the directions on the walls of the container in which it is kept. Thus,
Pressure of gas = force of gas exerts on walls of container / surface area of container

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