The Behavior of Gases

Directions for Monday 2/12/18: You will have your quiz tomorrow. I will review with you for a short while before the quiz. Copy as much of the notes as possible. You must copy anything that is underlined. I will be back in school tomorrow! Have a great day!

The Behavior of Gases The behavior of gases rely heavily on the properties of: Pressure Temperature moles volume.

Think of Chem 1A…. What do you remember about gases???? How do they differ from liquids and solids?

Pressure & Force Pressure (P) is defined as the force per unit of area on a surface. Atmospheric pressure (atm) is the pressure exerted on an object due to the weight of the column of the air above it in the atmosphere. A barometer is a device used to measure atmospheric pressure.

Units of Pressure pascal (Pa) kilopascal (kPa) millimeters of mercury (mm Hg) torr (torr) barr (barr) pounds per square inch (psi or lbs/in2) atmosphere (atm) - This is the unit of pressure that we will use in chemistry. All pressure units must be converted to atmospheres

Relationships between units of pressure 1.0 atm = 760 mmHg 1.0 atm = 760 torr 1.0 atm = 1.0135 x 105 Pa 1.0 atm = 14.700 psi PRACTICE: Convert 78.9 psi to units of atm.

Review: What are the 4 properties of all gases? What is pressure? Where on Earth is atmospheric pressure the greatest?

Temperature A temperature is a numerical measure of hot and cold. There are three units of temperature measurement: Fahrenheit (˚F), Celsius (˚C), Kelvin (K) We will measure or calculate temperature in units of Kelvin, not Celsius. K = °C + 273.15

Use the equation: K = ˚C + 273 Example Convert 30 degrees C to Kelvin. Use the equation: K = ˚C + 273

Volume A gas’ volume can change; gases can be compressed or expanded. Units of liters (L). Remember, there are 1000 mL in 1L.

Standard Temperature and Pressure Abbreviated as STP Standard temperature is equal to 0 °C, which is 273.15 K. Standard Pressure is 1 Atm YOU MUST MEMORIZE THAT STP IS 273.15K AND 1 ATM.

Direct Relationship vs. Inverse Relationship Direct Relationship: both variables increase together or both variables decrease together. Inverse Relationship: one variable increases while the other variable decreases or vice versa.

The Gas Laws Boyle’s Law: the pressure-volume relationship of gases Boyle’s Law states that the volume of a fixed mass of a gas at a constant temperature varies inversely with its pressure. P1V1 = P2V2

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

On your own: What pressure is required to compress 196.0 liters of air at 1.00 atmosphere into a cylinder whose volume is 26.0 liters? A gas occupies 12.3 liters at a pressure of 40.0 mm Hg. What is the volume when the pressure is increased to 60.0 mm Hg? (Watch the units!)  

The Gas Laws Charles’ Law: the Volume-Temperature relationship Charles’ Law states that the volume of a fixed mass of gas held at a constant pressure varies directly with its Kelvin temperature. V1 = V2 T1 T2

Problem #2 A gas has an initial volume of 752 mL at a temperature of 25 degrees C. The gas is heated to 100 degrees C. What is the new volume?

On your own…. Some students believe that teachers are full of hot air. If I inhale 2.2 liters of gas at a temperature of 18C and it heats to a temperature of 38C in my lungs, what is the new volume of the gas?   How hot will a 2.3 L balloon have to get to expand to a volume of 400 L? Assume that the initial temperature of the balloon is 25C.

The Gas Laws Gay-Lussac’s Law: the pressure-temperature relationship in gases Gay-Lussac’s Law states that the pressure of a fixed mass of a gas held at a constant volume will vary directly with its Kelvin temperature. P1 = P2 T1 T2

Problem #3 A gas has an initial temperature of 120 degrees C with a pressure of 1.07 atm. The gas is heated to a temperature of 205 degrees Celsius. What is the new pressure?

On your own… Determine the pressure change when a constant volume of gas at 1.00 atm is heated from 20.0 °C to 30.0 °C. If a gas is cooled from 323.0 K to 273.15 K and the volume is kept constant what final pressure would result if the original pressure was 750.0 atm?

The Gas Laws The Combined Gas Law The combined gas law expresses the relationship between pressure, volume, and the Kelvin temperature of a fixed amount of gas. (This means that the number of moles is held constant) P1V1 = P2V2 T1 T2

Problem #4 V1 = 27.5 mL P1 = 0.974 atm T1 = 22˚C V2 = ? P2 = 0.993 atm T2 = 15˚C

1. If 10L of oxygen at STP are heated to 512 ºC, what will be the new volume of gas if the pressure is also increased to 1520.0 mmHg? 2. What pressure is required to compress 196.0 liters of air at 1.00 atmosphere into a cylinder whose volume is 26.0 liters? 3. A gas occupies 12.3 liters at a pressure of 40.0 mm Hg. What is the volume when the pressure is increased to 60.0 mm Hg? 4. 2L of hydrogen, originally at 25.0 ºC and 750mmHg, is heated until a volume of 20L and a pressure of 3.5 atm is reached. What is the new temperature?

The Ideal Gas Law The ideal gas law is the mathematical relationship among pressure, temperature, volume, and the number of moles of a gas. PV = nRT P = pressure V = volume n = # moles R = ideal gas constant T = Kelvin temperature .

Problem #5 Calculate the grams of CO2 that would occupy a volume of 22.4 liters at STP.