General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 7 Gases 7.1 Properties of Gases Lectures © 2013 Pearson Education, Inc.

Common Gases Of the elements on the periodic table, some exist as a gas at room temperature, these include the Noble Gases, Group 8A (18), H2, N2, O2, F2, Cl2, and many oxides of nonmetals such as CO, CO2, NO, NO2, SO2, and SO3. 2

Gases and Environmental Concerns Some gases are responsible for environmental and health concerns including methane, CH4,and carbon dioxide, CO2  both greenhouse gases involved in climate change chlorofluorocarbons (CFCs)  involved in depleting the ozone layer, which filters out UV light reaching Earth, nitrogen oxides found in smog (respiratory irtitants), and volatile organic compounds (VOCs), such as compounds found in paint thinners, plastics, industrial solvents, pesticides 3

Kinetic Theory of Gases A gas consists of small particles that move randomly with high velocities. have essentially no attractive (or repulsive) forces toward each other. have a very small volume compared to the volume of the containers they occupy. are in constant motion. have kinetic energies that increase with an increase in temperature. 4

Properties of Gases Gases are described in terms of four properties: 1. pressure (P), 2. volume (V), 3. temperature (T), and 4. amount (n). 5

Gas Pressure Gas pressure is the force acting on a specific area. has units of atm, mmHg, torr, lb/in.2, and kilopascals(kPa). 1 atm = 760 mmHg (exact) 1 atm = 760 torr (exact) 1 atm = 14.7 lb/in.2 1 atm = 101.325 kPa 6

1. Pressure and Volume Relationship General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake The Original Gas Laws 1. Pressure and Volume Relationship (Boyle’s Law) © 2013 Pearson Education, Inc.

Boyle’s Law –oldest gas law Boyle’s law states that the pressure of a gas is inversely related to its volume when temperature (T) and amount of gas (n) are constant. if the pressure (P) increases, then the volume (V) decreases. 8

PV Constant in Boyle’s Law the product P × V is constant as long as T and n do not change. it can be stated that since P × V is a constant. P1V1 = P2V2 (T, n constant) 9

Guide to Using Gas Laws 10

Solving for a Gas Law Factor A sample of nitrogen gas (N2) has a volume of 4.2 L at 1.0 atm. If the pressure is decreased to 0.75 atm with no change in the temperature or amount of gas, what will be the new volume? Step 1 Organize the data in a table of initial and final conditions. Analyze the Problem. Factors T and n remain constant. Conditions 1 Conditions 2 Know Predict V1 = 4.2 L V2 = ? V increases P1 = 1.0 atm P2 = 0.75 atm P decreases 11

Solving for a Gas Law Factor A sample of nitrogen gas (N2) has a volume of 4.2 L at 1.0 atm. If the pressure is decreased to 0.75 atm with no change in the temperature or amount of gas, what will be the new volume? Step 2 Rearrange the gas law equation to solve for the unknown quantity. P1V1 = P2V2 Boyle’s Law To solve for V2 , divide both sides by P2. 12

Solving for a Gas Law Factor A sample of nitrogen gas (N2) has a volume of 4.2 L at 1.0 atm. If the pressure is decreased to 0.75 atm with no change in the temperature or amount of gas, what will be the new volume? Step 3 Substitute values into the gas law equation and calculate. 13

Boyle’s Law and Breathing: Inhalation During inhalation, the lungs expand, the pressure in the lungs decreases, and air flows towards the lower pressure in the lungs. 14

Boyle’s Law and Breathing: Exhalation During exhalation, lung volume decreases, pressure within the lungs increases, and air flows from the higher pressure in the lungs to the outside. 15

2. Temperature and Volume Relationship General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake The Gas Laws 2. Temperature and Volume Relationship (Charles’ Law) © 2013 Pearson Education, Inc.

Charles’s Law Charles’s law states that, the Kelvin temperature of a gas is directly related to the volume of the gas, P and n are constant, and as the temperature of a gas increases, the molecules move faster and its volume increases to maintain constant P. 17

Charles’s Law: V and T Charles’s law states that when the temperature of a gas increases, making the molecules move faster, the volume of the gas must increase to maintain constant pressure. 18

Charles’s Law: V and T A sample of neon gas has a volume of 3.1 L and a temperature of 12 ˚C. Find the new volume (L) of the gas if the temperature rises to 32 ˚C. Assume the pressure and amount of gas remain constant. Step 1 Organize the data in a table of initial and final conditions. Analyze the Problem. Conditions 1 Conditions 2 Know Predict T1 = 12 °C + 273 = 285 T1 = 32 °C+ 273 = 305 K T increases V1 = 3.1 L V1 = ? V increases 19

Charles’s Law: V and T A sample of neon gas has a volume of 3.1 L and a temperature of 12 ˚C. Find the new volume (L) of the gas if the temperature rises to 32 ˚C. Assume the pressure and amount of gas remain constant. Step 2 Rearrange the gas law equation to solve for the unknown quantity. 20

Charles’s Law: V and T A sample of neon gas has a volume of 3.1 L and a temperature of 12 ˚C. Find the new volume (L) of the gas if the temperature rises to 32 ˚C. Assume the pressure and amount of gas remain constant. Step 3 Substitute values into the gas law equation and the table. 21

3. Temperature and Pressure Relationship General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake The Gas Laws 3. Temperature and Pressure Relationship (Gay-Lussac’s Law) © 2013 Pearson Education, Inc.

Gay-Lussac’s Law: P and T Gay-Lussac’s law states that the pressure exerted by a gas is directly related to the Kelvin temperature. V and n are constant. an increase in temperature increases the pressure of a gas. 23

Calculation with Gay-Lussac’s Law A gas has a pressure at 2.0 atm at 18 ˚C. What is the new pressure when the temperature is increased to 62 ˚C? (V and n constant) Step 1 Organize the data in a table of initial and final conditions. Analyze the Problem. Conditions 1 Conditions 2 Know Predict P1 = 2.0 atm P2 = ? P increase T1 = 18 °C + 273 = 291 K T2 = 62 °C + 273 = 335 K T increase 24

Calculation with Gay-Lussac’s Law A gas has a pressure at 2.0 atm at 18 ˚C. What is the new pressure when the temperature is increased to 62 ˚C? (V and n constant) Step 2 Rearrange the gas law equation to solve for the unknown quantity. 25

Calculation with Gay-Lussac’s Law A gas has a pressure at 2.0 atm at 18 ˚C. What is the new pressure when the temperature is increased to 62 ˚C? (V and n constant) Step 3 Substitute values into the gas law equation and calculate. 26

General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake The Combined Gas Law © 2013 Pearson Education, Inc.

Combined Gas Law The combined gas law uses Boyle’s Law, Charles’s Law, and Gay-Lussac’s Law (n is constant). 28

Combined Gas Law By using the combined gas law, we can derive any of the gas laws by omitting those properties that do not change. 29

Using the Combined Gas Law A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm (n constant)? Step 1 Organize the data in a table of initial and final conditions. Analyze the Problem. Conditions 1 Conditions 2 P1 = 0.800 atm P2 = 3.20 atm V1 = 0.180 L V2 = 90.0 mL= 0.0900 L T1 = 29 °C + 273 = 302 K T2 = ? 30

Using the Combined Gas Law A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm (n constant)? Step 2 Rearrange the gas law equation to solve for the unknown quantity. 31

Using the Combined Gas Law A 0.180 L sample of gas has a pressure of 0.800 atm at 29 °C. At what temperature (°C) will the gas have a volume of 90.0 mL and a pressure of 3.20 atm (n constant)? Step 3 Substitute values to solve for unknown.

Learning Check A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)? 33

Solution A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)? Step 1 Organize the data in a table of initial and final conditions. Analyze the Problem. 34

Solution A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)? Step 2 Rearrange the gas law equation to solve for the unknown quantity. 35

Solution A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at −95 °C and a pressure of 802 mmHg (n constant)? Step 3 Substitute values into the gas law equation and calculate. 36