CHEM103 Chapter Notes - Chapter 6: Blaise Pascal, Pressure Measurement, Torr

Learning Goal: To be able to predict and calculate properties of real gases. Kinetic molecular theory makes certain assumptions about gases that are, in fact, not true for real gases. Therefore, the measured properties of a gas are often slightly different from the values predicted by the ideal gas law. The van der Waals equation is a more exact way of calculating properties of real gases. The formula includes two constants, a and 6, that are unique for each gas. The van der Waals equation is (p + an^2/V^2) (V - nb) = nRT, where P is the pressure, n the number of moles of gas, V the volume, T the temperature, and R the gas constant. All real gases possess intermolecular forces that can slightly decrease the observed pressure. In the van der Waals equation, the variable P is adjusted to P + an^2/V^2, where a is the attractive force between molecules. The volume of a gas is defined as the space in which the gas molecules can move. When using the ideal gas law we make the assumption that this space is equal to the volume of the container. However, the gas molecules themselves take up some space in the container. So in the van der Waals equation, the variable V is adjusted to be the volume of the container minus the space taken up by the molecules, V - nb, where b is the volume of a mole of molecules. 14.0 moles of gas are in a 5.00 L tank at 20.7 degree C. Calculate the difference in pressure between methane and an ideal gas under these conditions. The van der Waals constants for methane are a = 2.300 L^2 middot atin/mol^2 and b = 0.0430 L/mol Express your answer with the appropriate units.

Gases are different from solids and liquids. In a sample of gas, the molecules are far apart. The gas molecules also move around and collide with each other as well as with the walls of the container. These collisions generate pressure. The pressure of gas can be measured in different units. One convenient unit of measure is called the atmosphere (atm) because it is based on atmospheric pressure. At sea level, the average pressure is 1 atm. As you get higher in attitude, the pressure steadily drops until you leave the atmosphere, where t5he pressure is very close to 0 atm. The table below shows the different commonly used units of measuring gas pressure. Use this table in the pressure unit conversation: Convert 1.10 atm of pressure to its equivalent in millimeters of mercury. Express the pressure numerically in millimeters of mercury. The pressure in car tires is often measured in pounds per square inch (lb/in ^2) with the recommended pressure being in the range of 25 to 45 b/in.^3. Suppose a tire has a pressure of 25.5 lb/in.^2. Convert 25.5 lb/in.^2 to its equivalent in atmosphere. Express the pressure numerically in atmospheres. High-pressure liquid chromatography (HPLC) is a method used in chemistry and biochemistry to purity chemical substances. The pressures used in this procedure range from around 500 kilopascals (500,000 Pa) to about 60,000 kPa (80,000 000 Pa). It is often convenient to know the pressure in If an HPLC procedure is running at a pressure of 1 90 times 10^Pa, what is its running pressure in torr? Express the pressure numerically in torr.