CHEM 120 Lecture Notes - Lecture 2: Mole Fraction, Chemical Equation, Kahoolawe

The ideal gas law describes the relationship among the pressure P, volume V, number of moles n, and absolute temperature T of an ideal gas. Here is the relationship expressed mathematically: PV = nRT where R is a proportionality constant. The units of R are determined by the units of pressure and volume used in the equation. When atm is used for pressure and L for volume, the appropriate R value is 0.0821 L middot atm/mol middot K. How many air molecules are in a 15.0 times 12.0 times 10.0 ft room? Assume atmospheric pressure of 1.00 atm, a room temperature of 20.0 degree C. and ideal behavior. Volume conversion: There are 28.2 liters in one cubic foot.

Units In Parts A through C, the quantities were already given with the appropriate units. However, you should always determine which unit is most appropriate for each quantity, then do any necessary conversions before substituting numbers into the formula. Part D gives an example of this type of situation. The ideal gas equation is PV = nRT where P is pressure, V is volume, n is the number of moles, R is a constant, and T is temperature. You are told that a sample of gas has a pressure of P = 855 torr, a volume of V = 8320 mL, and a temperature of T = 292 K. If you use R = 8.206 times 10^- 2 L middot atm/(K middot mol), which of the following conversions would be necessary before you could find the number of moles of gas, n, in this sample? Convert the pressure to atmospheres (atm). Convert the pressure to pascals (Pa). Convert the volume to cubic meters (m^3). Convert the volume to cubic meters (m^3). Convert the volume to liters (L). Convert the temperature to degrees Celsius (degree C) Convert the temperature to degrees Fahrenheit (degree F).

t Deriving Gas Law Formulas Learning Goal: To understand how to determine the appropriate formula for a given gas law problem. When you are unsure of which formula to use to solve a gas law problem, it is often helpful to make a chart of initial and final values of pressure P volume V, number of moles, n, and temperature T, as shown in the table Initial Final This type of chart will help you to determine which quantities are changing and which quantities remain the same. For example, use the formula Ph Vi PrV2 for the product of pressure and volume at two different points in time when pressure and volume are changing but the number of moles of gas and the temperature are constant. Here is how this formula is derived from the ideal gas law, PV nRT: 1. If n and T are constant, the entire quantity nRT is constant. 2. Therefore, PV is constant. 3. It follows that the quantity PV at any point in time will be the same value as at any other point in time. 4. Therefore Ph Vi 2 V2 Now imagine an experiment where your chart looks like this Initial Final P 2 atm 2 atm V 1.7 L 2.5 L m 0.45 mol 0.45 mol T 273 K It is clear that V and T are the quantities that are changing, while Pand n are constant. To put a constants P, n, and R ogether, we need to do a little bit of algebra: n RT 2. TV 4. T s constant. 5. Therefore the quantity V/T at any point in time will be the same value as at any other point in time, so