Basic Chemistry Chapter 11 Gases Chapter 11 Lecture Fourth Edition Chapter 11 Gases 11.5 Temperature and Pressure (Gay-Lussac’s Law) Learning Goal When the Kelvin temperature of a gas is doubled at constant volume and amount of gas, the pressure also doubles.

Gay-Lussac’s law states the pressure (P) of a gas is directly related to its temperature (K) when V and n are constant if the pressure (P) increases, then the temperature (K) also increases Figure 11.6 Gay-Lussac’s law: When the Kelvin temperature of a gas is doubled at constant volume and amount of gas, the pressure also doubles.

Gay-Lussac’s Law Gay-Lussac’s law is a direct relationship between pressure and temperature. No change in number of moles and volume. All temperatures used in gas law calculations must be converted to Kelvin (K) temperature.

Gay-Lussac’s Law Equation The equation for Gay-Lussac’s law can be rearranged to solve for any factor. To obtain P2, multiply both sides by T2.

Learning Check A gas has a pressure of 2.0 atm at 18 °C. What is the new pressure when the temperature is 62 °C (V and n constant)?

Solution A gas has a pressure of 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. We can predict that as T increases, P increases. Conditions 1 Conditions 2 P1 = 2.0 atm P2 = ? T1 = 18 oC = 291 K T2 = 62 oC = 335 K

Solution A gas has a pressure of 2.0 atm at 18 °C. What is the new pressure when the temperature is 62 °C (V and n constant)? Step 2 Rearrange the gas law equation to solve for the unknown quantity. Solve Gay-Lussac’s law for P2.

Solution A gas has a pressure of 2.0 atm at 18 °C. What is the new pressure when the temperature is 62 °C (V and n constant)? Step 3 Substitute values into gas law equation and calculate.

Use the gas laws to complete with: increases or decreases. Learning Check Use the gas laws to complete with: increases or decreases. A. Pressure ______ when T decreases. B. When T decreases, P ______. Pressure ______ when T changes from 12 L to 24 L. Pressure _______ when T changes from 45 °C to 15 °C. Basic Chemistry Copyright © 2014 Pearson Education, Inc.

Use the gas laws to complete with: increases or decreases. Solution Use the gas laws to complete with: increases or decreases. A. Pressure decreases when T decreases. B. When T decreases, P decreases. Pressure increases when T changes from 12 L to 24 L. Pressure decreases when T changes from 45 °C to 15 °C. Basic Chemistry Copyright © 2014 Pearson Education, Inc.

Learning Check A gas has a pressure of 0.750 atm at 128 °C. What is the temperature in Celsius if the pressure increases to 1.50 atm (n and V remain constant)?

Solution A gas has a pressure of 0.750 atm at 128 °C. What is the temperature in Celsius if the pressure increases to 1.50 atm (n and V remain constant)? Step 1 Organize the data in a table of initial and final conditions. We can predict that as P increases, T increases. Conditions 1 Conditions 2 P1 = 0.750 atm P2 = 1.50 atm T1 = 128 oC = 401 K T2 = ?

Solution A gas has a pressure of 0.750 atm at 128 °C. What is the temperature in Celsius if the pressure increases to 1.50 atm (n and V remain constant)? Step 2 Rearrange the gas law equation to solve for the unknown quantity. Solve Gay-Lussac’s law for T2. Increasing temperature increases the pressure when moles and volume are constant.

Solution A gas has a pressure of 0.750 atm at 128 °C. What is the temperature in Celsius if the pressure increases to 1.50 atm (n and V remain constant)? Step 2 Rearrange the gas law equation to solve for the unknown quantity.

Solution A gas has a pressure of 0.750 atm at 128 °C. What is the temperature in Celsius if the pressure increases to 1.50 atm (n and V remain constant)? Step 3 Substitute values into the gas law equation and calculate. When T decreases, P also decreases.

Vapor Pressure and Boiling Point is the pressure above a liquid at equilibrium in a closed container at the boiling point vapor pressure becomes equal to the external pressure

Boiling Point of Water The boiling point of water depends on the vapor pressure is lower at higher altitudes

Boiling Point of Water An autoclave used to sterilize equipment attains a temperature higher than 100 °C. Increasing the pressure increases the temperature.