Chapter 13: Gases

What Are Gases? Gases have mass Gases have mass Much less compared to liquids and solids Much less compared to liquids and solids

Properties of Gases Gases are easy to compress Gases are easy to compress Liquids and solids are difficult to compress Liquids and solids are difficult to compress

What Are Gases? Gases fill their containers completely Gases fill their containers completely Liquids and solids have fixed volumes Liquids and solids have fixed volumes

What Are Gases? Gases move very quickly Gases move very quickly Movement of gases is called diffusion Movement of gases is called diffusion

What Are Gases? Gases exert pressure Gases exert pressure Pressure due to collisions Pressure due to collisions

Kinetic Molecular Theory The behavior of gas is explained by the Kinetic – Molecular theory of matter The behavior of gas is explained by the Kinetic – Molecular theory of matter 1. Gases consist of particles that have mass Gases are either monoatomic, diatomic, or polyatomic. Gases are either monoatomic, diatomic, or polyatomic.

Kinetic Molecular Theory 2. There are large distances between gas particles –Volume of particles is assumed to be zero compared to the total volume 3. Gas particles are in constant random motion

Kinetic Molecular Theory 4. Collisions of gas particles with other particles or with the walls of the container are completely elastic. Elastic collision

Kinetic Molecular Theory 5. Kinetic energy of gas depends upon temperature –High temperature, high KE –Low temperature, low KE 6. Gas particles exert no attractive forces between one another

Describing Behavior of Gases Depends upon 4 variables Depends upon 4 variables 1. Amount of Gas (n) – Measured in Moles (mol) 2. Volume (V) – Measure in Liters (L) 3. Temperature (T) – Measured in Kelvin (K) 4. Pressure (P) – Measured in Pascals (Pa)

Pressure Pressure is the amount of force per given area Pressure is the amount of force per given area P = F/A P = F/A One newton of force per square meter is the Pascal One newton of force per square meter is the Pascal Often measure in kPa Often measure in kPa

Atmospheric Pressure Pressure exerted by the atmosphere Pressure exerted by the atmosphere

Atmospheric Pressure Air Pressure measured by a barometer Air Pressure measured by a barometer Measured in mmHg Measured in mmHg

Atmospheric Pressure Air pressure changes with altitude Air pressure changes with altitude

Atmospheric Pressure Air pressure changes due to the heating by the sun Air pressure changes due to the heating by the sun

Manometer Enclosed gases may be measured by a manometer Enclosed gases may be measured by a manometer Pressure of gas = height + air pressure Pressure of gas = height + air pressure

Units of Pressure millibars (mb) = kPa = 1 atmosphere (atm) = 14.7 pounds per in 2 (psi) = 760 mm of Hg (torr) millibars (mb) = kPa = 1 atmosphere (atm) = 14.7 pounds per in 2 (psi) = 760 mm of Hg (torr)

Practice High Pressure 1085 mb in Mongolia (2001) Convert to kPa High Pressure 1085 mb in Mongolia (2001) Convert to kPa Low Pressure 870 mb in a Pacific Typhoon (1979) Convert to Atm Low Pressure 870 mb in a Pacific Typhoon (1979) Convert to Atm

Boyle’s Law The pressure and volume of a sample of gas are inversely proportional at constant temperature The pressure and volume of a sample of gas are inversely proportional at constant temperature “spring of air” “spring of air” P 1 V 1 =P 2 V 2 P 1 V 1 =P 2 V 2

Practice A weather balloon contains 150. L of gas, internal gas pressure is 1.0 atm. Atmospheric pressure at 41 km is 0.4 atm. Calculate the new volume of the balloon. A weather balloon contains 150. L of gas, internal gas pressure is 1.0 atm. Atmospheric pressure at 41 km is 0.4 atm. Calculate the new volume of the balloon L of a gas is at mmHg pressure. What is its volume at standard pressure? 2.00 L of a gas is at mmHg pressure. What is its volume at standard pressure?

Charles’s Law At constant pressure, the volume of a fixed amount of gas is directly proportional to its temperature. At constant pressure, the volume of a fixed amount of gas is directly proportional to its temperature. Helped determine absolute zero Helped determine absolute zero V 1 /T 1 =V 2 /T 2 V 1 /T 1 =V 2 /T 2 All temperatures must be converted to Kelvin All temperatures must be converted to Kelvin

Practice What will be the volume of a gas sample at 355 K if its volume at 273 K is 8.57 Liters? What will be the volume of a gas sample at 355 K if its volume at 273 K is 8.57 Liters? At constant pressure a gas can be used as a thermometer. A sample of gas has a volume of 1 L at C. What is the temperature if the volume of the same gas is changed to 0.45 Liters? At constant pressure a gas can be used as a thermometer. A sample of gas has a volume of 1 L at C. What is the temperature if the volume of the same gas is changed to 0.45 Liters?

Avogadro's Law Avogadro’s Law states equal volumes of gases at the same temperature and pressure contain an equal number of particles. Avogadro’s Law states equal volumes of gases at the same temperature and pressure contain an equal number of particles. Molar volume 22.4 L at STP. Molar volume 22.4 L at STP.

Dalton’s Law Dalton’s Law of Partial Pressure states that the sum of the partial pressures of all of the components in a gas mixture is equal to the total pressure of the gas mixture. Dalton’s Law of Partial Pressure states that the sum of the partial pressures of all of the components in a gas mixture is equal to the total pressure of the gas mixture. P T = P a + P b + P c …. P T = P a + P b + P c ….

Practice What is atmospheric pressure if the partial pressures of N 2, O 2, and Ar are mm Hg, mm Hg, and 0.5 mm Hg respectively? What is atmospheric pressure if the partial pressures of N 2, O 2, and Ar are mm Hg, mm Hg, and 0.5 mm Hg respectively? The gases of carbon dioxide, oxygen, nitrogen, neon, and krypton are mixed in a container. All gases have the same partial pressure and the total pressure is 33,500 Pa. What is the partial pressure of nitrogen? The gases of carbon dioxide, oxygen, nitrogen, neon, and krypton are mixed in a container. All gases have the same partial pressure and the total pressure is 33,500 Pa. What is the partial pressure of nitrogen?

Ideal Gas vs. Real Gas An Ideal Gas represents a gas as described by the kinetic-molecular theory. An Ideal Gas represents a gas as described by the kinetic-molecular theory. Assumes no interaction between gas molecules Assumes no interaction between gas molecules All gases are Real Gas All gases are Real Gas An ideal gas behaves >95% like a real gas. An ideal gas behaves >95% like a real gas. Real Gases deviate from ideal gases at low temperatures and high pressures. Real Gases deviate from ideal gases at low temperatures and high pressures.

Ideal Gas Law The ideal gas law combines all variables involved in a gas. The ideal gas law combines all variables involved in a gas. PV = nRT R is a constant R is a constant R = atm-L/mol-K R = atm-L/mol-K Temp must be in K Temp must be in K Pressure must be in Atm Pressure must be in Atm Volume must be in Liters Volume must be in Liters

Practice How many moles of a gas at 100 o C does it take to fill a 1.00 Liter flask to a pressure of 1.50 atm? How many moles of a gas at 100 o C does it take to fill a 1.00 Liter flask to a pressure of 1.50 atm? What is the volume occupied by 9.45 g of C 2 H 2 at STP? What is the volume occupied by 9.45 g of C 2 H 2 at STP? How many kilograms of oxygen gas are contained in a sample that occupies 505 L at 675 kPa and -15 o C? How many kilograms of oxygen gas are contained in a sample that occupies 505 L at 675 kPa and -15 o C?