All gases, including the hot gases in a kiln, behave in a certain manner under external influences. A perfect gas is one that obeys very closely certain physical laws. All the gases are assumed to be perfect gas for the laws to observed.
All the calculations for pressure and temperature are done in absolute.
Example:
Temperature – 60oC = 60 + 273 = 333o absolute
Pressure – P = Px – Patm (P = Relative Pressure, Px = Absolute Pressure, Patm = standard atmospheric pressure
if the required pressure is (-)13 PSI, the ultimate pressure = (-)13 PSI + 14.696 PSI = 1.696 PSI
BOYLE’S LAW
“Under constant temperature, tl1e volume of a given mass of gas varies inversely as the pressure upon it.”
P1 = Initial pressure(absolute), P2 = Final pressure(absolute), V1 = volume at Pressure P1 and V2 = volume at pressure P2.
Example:
The volume of a gas with a pressure of 72 cm Hg is 20000 m3, what will be the volume at standard 76 cm Hg, keeping the temperature constant.
CHARLE’S LAW
“The volumes occupied by a given mass of gas at different temperatures are proportional to the absolute temperatures of the gas provided the pressure remains constant.”
All gases expand when the temperature is raised. If the temperature of a gas rise of 1o C will result in an expansion of (1/273) of the original volume.
V1 = Initial volume at T1, V2 = Final volume at T2, T1 = Initial temperature(absolute)
T2 = Final temperature (absolute).
Example:
Volume of a gas at 100oC is 5000 m3, what will be the volume of the same gas at 300oC. The pressure of the system remains same.
T1 = 100oC = 100 + 273 = 373oK
T2 = 300oC = 300 + 273 = 573oK
V1 = 5000 m3
GAY-LUSSAC’S LAW
“The pressure exerted by a given mass of gas will increase in proportion to the temperature if the volume is held constant. All unit again are in absolute values.”
P1 = Initial pressure at T1, P2 = Final pressure at T2, T1 = Initial temperature(absolute)
T2 = Final temperature (absolute).
Example:
Pressure of a gas at 1000oC is 65 cmHg, what will be the pressure of the same gas at 1300oC. The pressure of the system remains same.
T1 = 1000oC = 1000 + 273 =1273oK
T2 = 1300oC = 1300 + 273 = 1573oK
V1 = 5000 m3
GENERAL GAS LAW
P1, V1 and T1 are initial pressure, volume and temperature and P2, V2 and T2 are final pressure, volume and temperature. (With pressure and temperature measured in absolute unit).
Example: The volume of a gas at 76 mmHg pressure is 5000m3 and the temperature is 300oC. Volume of the gas at 70 mmHg and temperature of 700oC is
T1 = 300oC = 273+300 = 573oK
T2 = 700oC = 273+700 = 973oK
