Experiment 11 The Gas Laws
Introduction: In this experiment you will (1) determine whether Boyle’s Law applies to a mixture of gases (air) and (2) calculate the gas constant, R, by determining the volume of a known amount of gas (H2) at a measured temperature and pressure. Determination of Whether Boyle’s Law Applies to Air
Boyle’s Law states that for a fixed amount of gas at constant temperature, the pressure of the gas will vary inversely with the volume so that P ∝ 1/V or PV = a constant (if n and T are constant). To determine whether this relationship holds for a mixture of gases, the pressure of a fixed amount of air (which is a mixture of gases) will be measured as the volume of the air is varied while keeping the temperature of the air constant. Determination of the Gas Constant, R
The ideal gas law arises from several different gas laws. Boyle’s law describes the inverse relationship between pressure and volume, P ∝ 1/V, for a sample of gas at constant temperature. Charles’ law describes the direct relationship between volume and temperature, V ∝ T, for a sample of gas at a constant pressure. The Gay-Lussac law describes the direct relationship between pressure and temperature, P ∝ T, for a sample of gas at constant volume. Together these lead to what’s referred to as the combined gas law, used to relate the properties of a given sample of gas at two different sets of conditions, labeled 1 and 2. 11 22
PV = PV (1)
Note that all three of the gas laws are satisfied by this equation. For example, if temperature is constant, T1 = T2 so that T1 and T2 can be eliminated from the equation, leaving P1V1 = P2V2, which is Boyle’s Law. Another relationship between gas properties is Avogadro’s Principle. It states that for the case in which the pressure and temperature of a gas are held constant, the volume of the gas is proportional to the number of moles, or V ∝ n, or V/n = a constant. Adding this relationship to the combined gas law gives the following: 11 22...
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