1. Basic Chemistry Chapter 11 Gases Chapter 11 Lecture
Fourth Edition
Chapter 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.

2. 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.

3. 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.

4. 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.

5. 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)?

6. 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

7. 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.

8. 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.

9. 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 °C to 15 °C.
Basic Chemistry Copyright © 2014 Pearson Education, Inc.

10. 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 °C to 15 °C.
Basic Chemistry Copyright © 2014 Pearson Education, Inc.

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

12. Solution
A gas has a pressure of 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 = atm
P2 = 1.50 atm
T1 = 128 oC = 401 K
T2 = ?

13. Solution
A gas has a pressure of 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.

14. Solution
A gas has a pressure of 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.

15. Solution
A gas has a pressure of 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.

16. 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

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

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