Volumes and densities of gases vary significantly with changes in pressure and temperature. This means that measurements of the volumes of gases will likely vary from one laboratory to another. To correct for this, scientists have adopted a set of standard conditions of temperature and pressure (STP) as a reference point in reporting all measurements involving gases. They are 0°C (or 273 K) and 760mmHg or 1 atm (or 1.013×105 N m−2 in S.I. units). Therefore standard temperature and pressure, as used in calculations involving gases, are defined as 0°C (or 273 K) and 1 atmosphere (or 760 torr). (Note: For calculations involving the gas laws, temperature must be in K.) Boyle’s law states that the volume of a given mass of gas at constant temperature is inversely proportional to the pressure. The law can be expressed in mathematical terms: V α 1/P or PV = k at constant n and T Since P×V = constant, problems dealing with P–V relationships can be solved by using the simplified equation: P1V1 = P2V2 Here P1, V1 represent one set of conditions and P2, V2 represent another set of conditions for a given mass of gas. Charles’s law states that the volume of a given mass of gas is directly proportional to its absolute temperature. So if the absolute temperature is doubled, say from 300 K to 600 K, the volume of the gas will also double. A plot of the volume of a gas versus its temperature (K) gives a straight line. A notable feature of such a plot is that the volume of all gases extrapolates to zero at the same temperature, −273.2◦C. This point is defined as 0 K, and is called absolute zero. Thus, the relationship between the Kelvin and Celsius temperature scales is given as: K = 0°C + 273. Scientists believe that the absolute zero temperature, 0 K, cannot be attained, although some laboratories have reported producing 0.0001 K.
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