Drill 4/16/2015 What do you think is the oldest form of human flight? How does it work?

SWBAT Use the law of partial pressures to calculate partial pressures and total pressures of gases. Use Boyle’s Law to calculate volume-pressure changes at constant temperature. Use Charles’ Law to calculate volume-temperature changes at constant pressure.

Agenda Law of Partial Pressures Boyle’s Law Charles’ Law Online Lab

Think About It… What do you already know about gases? List 3 things you think you already know about gases. What pressure units used in gas measurements are you already familiar with? think about everyday practical instances for example, the weather on the local news or the pressure in a car tire

Common Units of Pressure atm (atmosphere) torr mm Hg inches Hg pascal (Pa) kilopascal (kPa) lb/in 2

Conversions 1 atm = 101,325 Pa (pascals) = kilopascals (kPa) 1 atm = 760 mm Hg = 760 torr 1 atm = lb/in 2 1 bar = 100,000 Pa = atm

Practice Problem The column of mercury in a barometer is 745 mm above the mercury reservoir at the bottom. What is the atmospheric pressure in pascals (Pa)?

Answer 99,325 Pa

To Try on Your Own... The air pressure inside the cabin of an airplane is 8.3 lb/in 2. What is this pressure in atmosphere units?

Answer 0.56 atm

The Gas Laws: Boyle’s Law & Charles’ Law

Kinetic-Molecular Theory Based on the idea that particles of matter are always in motion. Explains the three states of matter A model to explain the behavior of gases.

Kinetic-molecular Theory Particles in a gas sample are far enough apart that size has little influence on its volume.

Measuring Gases In order to describe a gas sample and make predictions about its behavior under different conditions, four variables are used: 1.amount of gas, 2. volume, 3. temperature, and 4. pressure.

Law of Partial Pressures The total pressure of a gas mixture is the sum of the pressures of the gases in the mixture. P T = P 1 + P 2 + P

Sample Problem What is the atmospheric pressure if the partial pressures of nitrogen, oxygen, and argon are mm Hg, mm Hg, and 0.5 mm Hg, respectively?

Answer mm Hg

Your Turn… A mixture of O 2, CO 2 and N 2 has a total pressure of 0.97 atm. What is the partial pressure of O 2 if the partial pressure of CO 2 is 0.70 atm and the partial pressure of N 2 is 0.12 atm?

Answer 0.15 atm

Boyle’s Law the pressure and volume of a fixed mass of gas at constant temperature are inversely proportional to each other P 1 V 1 = P 2 V 2 (equation form)

Sample Problem A gas at a pressure of 608 mm Hg is held in a container with a volume of 545 cm 3. The volume of the container is then increased to 1065 cm 3 without a change in temperature. Calculate the new pressure of the gas.

Answer 311 mm Hg

Practice Problem A balloon filled with helium gas has a volume of 500. mL at a pressure of 1 atm. The balloon is released and rises in altitude, where the pressure is 0.5 atm. If the temperature has remained the same, what volume does the gas occupy at this height?

Answer 1000 mL He

Charles’ Law The volume of a fixed mass of gas at constant pressure varies directly with the Kelvin temperature. V 1 T 2 = V 2 T 1 (equation form)

Important When solving gas law-type problems, the temperature value that you plug into the necessary equation must be in units of Kelvin (NOT Celsius)

Temperature Conversion To convert between Celsius and Kelvin: K = °C For example, 20°C = 293 K Note: The Kelvin scale is not a degree scale

Sample Problem What will be the volume of a gas sample at 355 K if its volume at 273 K is 8.57 L?

Answer 11.1 L

Practice Problem A sample of air has a volume of mL at 67°C. At what temperature would its volume be 50.0 mL at constant pressure?

Answer 121 K = - 152°C

The Combined Gas Law The combined gas law expresses the relationship between pressure, volume, and temperature of a fixed amount of gas (P 1 V 1 )/T 1 = (P 2 V 2 )/T 2 Or P 1 V 1 T 2 = P 2 V 2 T 1

Practice Prob #1 A helium-filled balloon has a volume of 50.0 L at 25°C and 1.08 atm. What volume will it have at atm and 10.0°C?

Answer 60.0 L He

Practice Prob #2 A gas has a volume of 1.75 L at - 23°C and kPa. At what temperature would the gas occupy 1.30 L at kPa?

Answer 260. K or - 13°C

Practice Prob #3 A sample of oxygen that occupies 1.00 x 10 6 mL at 575 mm Hg is subjected to a pressure of 1.25 atm. What will the final volume of the sample be if the temperature is held constant?

Answer 6.05 x 10 5 mL

Avogadro’s Law Equal volumes of gases at the same temperature and pressure contain equal numbers of particles. V 1 = V 2 n 1 n 2

Ideal Gas Law An “Ideal” Gas follows the gas laws under all conditions of temperature and pressure. This concept is used to model gas behavior A “Real” Gas does exist and has intermolecular forces, particle volume, and can change states.

Ideal Gas Law Calculations made using the ideal gas law are used to estimate experimental measurements. The ideal gas law is the mathematical relationship among pressure (P), volume (V), the number of moles of a gas (n), and temperature (T). PV = nRT (equation form)

The Gas Constant The constant “R” is known as the ideal gas constant R = (L-atm)/(mol-K)

Be Careful with Your Units P (must be in atm) V (must be in L) T (must be in K)

Sample Problem An engineer pumps 5.00 mol of carbon monoxide gas into a cylinder that has a capacity of 20.0 L. What is the pressure in kPa of CO inside the cylinder at 25°C?

Answer 619 kPa

Practice Prob 2 What volume would be occupied by grams of hydrogen gas at a pressure of 2.01 atmospheres and a temperature of 35.0°C?

Answer 4.09 L H 2

Drill # 163/13 &14/13 Convert 748 mm Hg to atm atm