Physical Properties of Gases
3. Temperature
Air balloon shrinks after submersion
in liquid nitrogen
The symbol used to represent temperature in equations is T with SI units of kelvins.
The speed of a gas particle is proportional to its absolute temperature. The volume of the balloon in the video shrinks when the trapped gas particles slow down with the addition of extremely cold nitrogen. The temperature of any physical system is related to the motions of the particles (molecules and atoms) which make up the [gas] system.[10] In statistical mechanics, temperature is the measure of the average kinetic energy stored in a particle. The methods of storing this energy are dictated by the degrees of freedom of the particle itself (energy modes). Kinetic energy added (endothermic process) to gas particles by way of collisions produces linear, rotational, and vibrational motion. In contrast, a molecule in a solid can only increase its vibrational modes with the addition of heat as the lattice crystal structure prevents both linear and rotational motions. These heated gas molecules have a greater speed range which constantly varies due to constant collisions with other particles. The speed range can be described by the Maxwell-Boltzmann distribution. Use of this distribution implies ideal gases near thermodynamic equilibrium for the system of particles being considered. |
4. Amount of Gas
The amount of gas present is measured in moles (mol) or in grams (g). Grams will need to be converted to moles at some point. When the generalized variable of amount in moles is discussed, the letter "n" is used as the symbol (note: the letter is in lowercase. The others above are all caps.).
Standard Temperature and Pressure (STP) Standard Temperature of a gas is 0°C or 273K. Standard pressure is 1 atm or 760 mm Hg. Standard Molar Volume of a Gas The volume of a gas is dependant on the temperature and pressure. If a fixed number of particles, in this case 6.02 x 10 23 particles, known collectively as 1 mole, are held at a constant temperature of 1 atm (760 mm Hg) and 0°C (273K) they will occupy a volume of exactly 22.4 liters. This volume is the same regardless of what gas sample is used; be it O2 or N2 or CO2 or C3H8. If 1 mole of any gas is at STP, it will occupy a volume of 22.4 Liters. This is a convenient relationship to know when working with gas laws and calculations. Abbreviations Conversions atm - atmosphere K = °C + 273 mm Hg - millimeters of mercury 1 cm 3 (cubic centimeter) = 1 mL (milliliter) torr - another name for mm Hg 1 dm 3 (cubic decimeter) = 1 L (liter) = 1000 mL Pa - Pascal (kPa = kilo Pascal) Standard Conditions K - Kelvin 0.00 °C = 273 K °C - degrees Celsius 1.00 atm = 760.0 mm Hg = 101.325 kPa = 101,325 Pa |