Definition of Terms used to Describe the Behaviour of Gases
The following terms are generally used to describe the behaviour of gases.
The volume of a gas is the space it occupies. The SI unit for volume is cubic metre, m3, Cubic decimetre dm3, and cubic centimetre cm3 are commonly used. For conversion: 1.0dm3 = 1000cm3.
Temperature is a measure of the degree of hotness or coldness of a body. It is measured by the use of a thermometer. Temperature is measured in Celsius or centigrade scale, and also Kelvin temperature.
The Celsius or centigrade temperature scale uses the freezing point of water 00C as its starting point. The Kelvin temperature scale has -2730C as the starting point. Kelvin temperature also known a absolute temperature is higher than Celsius temperature by 273 degrees. Thus, 00C on Celsius or centigrade scale is 273k on the absolute or Kelvin temperature scale.
00C = 273k, -2730C = 0k
To convert a Celsius temperature (00C) to a Kelvin temperature (K), add 273
i.e k = 00C +273
to convert Kelvin temperature (k) to Celsius temperature (00C), subtract 273 from Kelvin temperature
00C = k – 273
Convert the following Celsius temperatures to Kelvin temperatures
(a) 1220C (b) -1320C (c) 00C
Formula K = 0C + 273
(a) 1220C = (122 +273)k = 395k
(b) -1320C = (-132 +273)k = 141k
(c) 00C = (0 +273)k = 273k
Convert the following Kelvin temperature to Celsius temperatures
(a) 155k (b) 294k (c) 525k
Formula: 00C = k – 273
(a) 155k = (155 – 273)0C = -1180C
(b) 294k = (294 – 273)0C = 210C
(c ) 525k = (525 – 273)0C = 2520C
Pressure is defined as force per unit area. The SI unit of pressure is Newton per metre square.
Gas pressures are also expressed in atmosphere (atm). Gas pressures are also expressed in Pascals (Pa) and also in millimetre mercury (mmHg).
Standard Temperature and Pressure s.t.p
A reference temperature and pressure has been arbitrarily adopted as standard. Standard temperature is 00C or 273k.
Standard pressure is 760 millimetres of mercury (760mmHg) or 1.01 x 105 Newton per metre square (1.01 x 105 Nm-2) or 1 atmospheric pressure (1atm) or 101325 Pascals (101325Pa).