CHEM 5013 Applied Chemical Principles Chapter Five Professor Bensley Alfred State College

Chapter Objectives Describe the physical properties of gases. Describe the physical properties of gases. Use the ideal gas law for calculating changes in the conditions of gases. Use the ideal gas law for calculating changes in the conditions of gases. Use the concept of partial pressure to work with mixtures of gases. Use the concept of partial pressure to work with mixtures of gases. Perform stoichiometric calculations for reactions involving gases as reactants or products. Perform stoichiometric calculations for reactions involving gases as reactants or products.

Properties of Gases

Pressure Pressure: Pressure:

Gas Pressure Pressure is the result of molecular collisions between gas molecules and container walls. Pressure is the result of molecular collisions between gas molecules and container walls. A barometer is used to measure pressure. A barometer is used to measure pressure.

Units of Pressure and STP 1 torr = 1 mm Hg 1 torr = 1 mm Hg 1 atm = 760 torr = 760 mm Hg (exactly) 1 atm = 760 torr = 760 mm Hg (exactly) 1 atm = 101,325 Pa (exactly) 1 atm = 101,325 Pa (exactly) 1 atm = 14.7 psi 1 atm = 14.7 psi At sea level, atmospheric pressure is? At sea level, atmospheric pressure is? Standard Temperature and Pressure Conditions (STP): Standard Temperature and Pressure Conditions (STP):

Empirical Gas Laws Gases behave simply under “moderate” conditions with respect to four things: Gases behave simply under “moderate” conditions with respect to four things: 1) 1) 2) 2) 3) 3) 4) 4)

Boyle’s Law PV = constant P1V1 P1V1 P1V1 P1V1 = P2V2P2V2P2V2P2V2 For a given amount of gas at a constant temp. Charles’s Law V/T = V 1 V 1 / T 1 =V 2 T 1 =V 2 / T2T2T2T2 For a given amount of gas at a given pressure WARNING – Temperature must be absolute (Kelvin Units) for ALL gas laws.

Examples A volume of oxygen gas occupies 38.7 mL at 751 mm Hg at 21°C. What is the volume if the pressure changes to 359 mm Hg and temp. remains constant? A volume of oxygen gas occupies 38.7 mL at 751 mm Hg at 21°C. What is the volume if the pressure changes to 359 mm Hg and temp. remains constant? You prepared carbon dioxide by adding HCl(aq) to marble chips (CaCO 3 ). According to your calculations, you should obtain 79.4 mL of CO 2 at 0°C and 760 mm Hg. How many milliliters of gas would you obtain at 27°C? You prepared carbon dioxide by adding HCl(aq) to marble chips (CaCO 3 ). According to your calculations, you should obtain 79.4 mL of CO 2 at 0°C and 760 mm Hg. How many milliliters of gas would you obtain at 27°C?

Combined Gas Law PV = constant P 1 V 1 = P 2 V 2 PV = constant P 1 V 1 = P 2 V 2 T T 1 T 2 T T 1 T 2 (for a given molar amount of gas) (for a given molar amount of gas)Example: Divers working from a North Sea oil drilling platform experience pressures of 5.0x10 1 atm at a depth of 5.0x10 2 m. If a balloon is inflated to a volume of 5.0L (the volume of a lung) at that depth at a water temperature of 4.0°C, what would the volume of the balloon be on the surface (1.0 atm pressure) at a temperature of 11°C?

Avogadro’s Law Relates volume and molar amount. Relates volume and molar amount. One mole of any gas contains how many molecules? One mole of any gas contains how many molecules? At STP, V m = At STP, V m =

Ideal Gas Law We can combine the empirical gas laws into one equation called the Ideal Gas Law We can combine the empirical gas laws into one equation called the Ideal Gas Law There must be a proportionality constant that governs relationships of Empirical Gas Laws = R There must be a proportionality constant that governs relationships of Empirical Gas Laws = R R is the universal gas law constant. R is the universal gas law constant. R = L atm/mol K R = L atm/mol K

The Ideal Gas Law The ideal gas law is the quantitative relationship between pressure, volume, moles gas present, and the absolute temperature. The ideal gas law is the quantitative relationship between pressure, volume, moles gas present, and the absolute temperature. Units are critical! Units are critical!

Ideal Gas Law Examples and Applications  A 50.0-L cylinder of nitrogen, N 2, has a pressure of 17.1 atm at 23°C. What is the mass of nitrogen in the cylinder?  What is the density of methane gas (natural gas), CH 4, at 125°C and 3.50 atm?

Gas Stoichiometry Example: The following reaction can be used to produce pure oxygen gas: 2 H 2 O 2 (l)  2 H 2 O (l) + O 2 (g) Suppose I used 0.01 moles of H 2 O 2. How many liters of oxygen gas will I get at 298K and 1 atm?

Gas Stoichiometry Example: How many liters of chlorine gas, Cl 2, can be obtained at 40°C and 787 mmHg from 9.41 grams of HCl according to the following reaction? 2 KMnO 4 (s) + 16 HCl (l)  8 H 2 O (l) + 2 KCl (aq) + 2 MnCl 2 (aq) + 5 Cl 2 (g)

Dalton’s Law of Partial Pressures

Partial pressure – Dalton’s Law of Partial Pressures – P T = P A + P B + P C + …

Calculation of Partial Pressure of Gas in a Mixture A mL sample of air exhaled from the lungs is analyzed and found to contain g N 2, g O 2, g CO 2, and g water vapor at 35°C. What is the partial pressure of each component and the total pressure of the sample?