Basic Chemistry Copyright © 2011 Pearson Education, Inc. 1 Chapter 11 Gases 11.5 Temperature and Pressure (Gay-Lussac’s Law) An autoclave used to sterilize equipment attains a temperature higher than 100 °C.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 2 Gay-Lussac’s Law: P and T In Gay-Lussac’s law, the pressure exerted by a gas is directly related to the Kelvin temperature V and n are constant P 1 = P 2 T 1 T 2

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 3 Learning Check Solve Gay-Lussac’s law for P 2. P 1 = P 2 T 1 T 2

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 4 Solution Solve Gay-Lussac’s law for P 2. P 1 = P 2 T 1 T 2 Multiply both sides by T 2 and cancel P 1 x T 2 = P 2 x T 2 T 1 T 2 P 2 = P 1 x T 2 T 1

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 5 A gas has a pressure at 2.0 atm at 18 °C. What is the new pressure when the temperature is 62 °C (V and n constant)? STEP 1 Organize the data in a table of initial and final conditions. Conditions 1 Conditions 2 Know Predict P 1 = 2.0 atm P 2 = ? P increases T 1 = 18 °C T 2 = 62 °C T increases = 291 K = 335 K Example of Using Gay- Lussac’s Law

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 6 Example of Using Gay- Lussac’s Law (continued) STEP 2 Rearrange the gas law for the unknown. Solve Gay-Lussac’s law for P 2. P 1 = P 2 T 1 T 2 P 2 = P 1 T 2 T 1 STEP 3 Substitute values into the gas law to solve for the unknown. P 2 = 2.0 atm x 335 K = 2.3 atm 291 K Temperature ratio increases pressure

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 7 Use the gas laws to complete with 1) increases or 2) decreases. A. Pressure _______ when V decreases. B. When T decreases, V _______. C. Pressure _______ when V changes from 12 L to 24 L D. Volume _______when T changes from 15 °C to 45°C Learning Check

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 8 Use the gas laws to complete with 1) increases or 2) decreases. A. Pressure (1) increases when V decreases. B. When T decreases, V (2) decreases. C. Pressure (2) decreases when V changes from 12 L to 24 L D. Volume (1) increases when T changes from 15 °C to 45 °C Solution

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 9 Learning Check A gas has a pressure of 645 mmHg at 128 °C. What is the temperature in Celsius if the pressure increases to 1.50 atm (n and V remain constant)?

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 10 Solution STEP 1 Organize the data in a table of initial and final conditions. P 2 = 1.50 atm x 760 mmHg = 1140 mmHg 1 atm Conditions 1Conditions 2 Know Predict P 1 = 645 mmHg P 2 = 1140 mmHg P increases T 1 = 128 °C T 2 = K – 273 T increases = 401 K = ? °C

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 11 Solution (continued) STEP 2 Rearrange the gas law for the unknown. Solve Gay-Lussac’s law for T 2. P 1 = P 2 T 1 T 2 T 2 = T 1 x P 2 P 1 STEP 3 Substitute values into the gas law to solve for the unknown. T 2 = 401 K x 1140 mmHg = 709 K – 273 = 436 °C 645 mmHg Pressure ratio increases temperature

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 12 Vapor Pressure and Boiling Point Vapor pressure is the pressure above water at equilibrium in a closed container at the boiling point is equal to the external pressure

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 13 Boiling Point of Water The boiling point of water depends on the vapor pressure is lower at higher altitudes

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 14 Boiling Point of Water The boiling point of water is increased by using an autoclave to increase external pressure An autoclave used to sterilize equipment attains a temperature higher than 100 °C.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Learning Check In each of the following pairs of atmospheric and vapor pressure, indicate if water will or will not boil. Atmospheric Vapor Boiling PressurePressure Occurs? A. 760 mmHg760 mmHg B. 960 mmHg760 mmHg C. 520 mmHg620 mmHg 15

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Solution Atmospheric Vapor Boiling PressurePressure Occurs? A. 760 mmHg760 mmHg yes B. 960 mmHg760 mmHg no C. 520 mmHg620 mmHg yes 16