1) This document discusses Charles' Law and how it relates the volume of an ideal gas to its temperature when pressure is held constant. Charles' Law states that the volume of a gas is directly proportional to its absolute temperature. 2) An example problem demonstrates how to use the Charles' Law equation to calculate the volume of a gas at a different temperature given its initial volume and temperature. 3) Learning checks are included to test understanding of Charles' Law and how the volume and temperature of a gas are related at constant pressure.

1. Ideal gases: Charles’ Law
Krisan M. Luis
Instructor

2. Objectives
• To describe the behavior of ideal gases
– To understand the following gas laws
• Boyle’s Law
• Charles’ Law
• Avogadro’s Law
– To understand the ideal gas equation
– To apply the above concepts on real life situations

3. Kinetic Theory of Gases
The particles in gases
•
Are very far apart
•
Move very fast in straight lines until they collide
•
Have no attraction (or repulsion)
•
Move faster at higher temperatures

4. Charles’ Law
V = 125 mL
V = 250 mL
T = 273 K
T = 546 K
Observe the V and T of the balloons. How does
volume change with temperature?

5. Charles’ Law: V and T
At constant pressure, the volume of a gas is
directly related to its absolute (K) temperature
V1 = V2
T1
T2

6. Variation of gas volume with temperature
at constant pressure.
Charles’ Law
V
T
V = constant x T
V1/T1 = V2 /T2
Temperature must be
in Kelvin
T (K) = t (0C) + 273.15
5.3

7. Learning Check GL3
Use Charles’ Law to complete the statements below:
1. If final T is higher than initial T, final V
is (greater, or less) than the initial V.
2. If final V is less than initial V, final T is
(higher, or lower) than the initial T.

8. Solution GL3
V1 = V2
T1
T2
1. If final T is higher than initial T, final V
is (greater) than the initial V.
2. If final V is less than initial V, final T is (lower) than
the initial T.

9. A sample of carbon monoxide gas occupies 3.20 L at 125 0C. At what
temperature will the gas occupy a volume of 1.54 L if the pressure remains
constant?
V1 /T1 = V2 /T2
V1 = 3.20 L
V2 = 1.54 L
T1 = 398.15 K
T2 = ?
T1 = 125 (0C) + 273.15 (K) = 398.15 K
T2 =
V2 x T1
V1
=
1.54 L x 398.15 K
3.20 L
= 192 K
5.3

10. V and T Problem
A balloon has a volume of 785 mL
on a Fall day when the
temperature is 21°C. In the
winter, the gas cools to 0°C. What
is the new volume of the
balloon?

11. VT Calculation
Complete the following setup:
Initial conditions
Final conditions
V1 = 785 mL
V2 = ?
T1 = 21°C = 294 K T2 = 0°C = 273 K
V2 = _______ mL x __
V1
K = _______ mL
K
Check your answer: If temperature decreases,
V should decrease.

12. Learning Check GL4
A sample of oxygen gas has a volume of 420
mL at a temperature of 18°C. What
temperature (in °C) is needed to change the
volume to 640 mL?
1) 443°C 2) 170°C
3) - 82°C

13. Solution GL4
A sample of oxygen gas has a volume of 420
mL at a temperature of 18°C. What
temperature (in °C) is needed to change the
volume to 640 mL?
2) 170°C
T2 = 291 K x 640 mL = 443 K
420 mL
= 443 K - 273 K = 170°C

14. Gay-Lussac’s Law: P and T
The pressure exerted by a confined gas is
directly related to the temperature (Kelvin) at
constant volume.
P (mm Hg)
T (°C)
936
761
691
100
25
0

15. Learning Check GL5
Use Gay-Lussac’s law to complete the statements
below:
1. When temperature decreases, the
pressure of a gas (decreases or increases).
2. When temperature increases, the pressure
of a gas (decreases or increases).

16. Solution GL5
1. When temperature decreases, the
pressure of a gas (decreases).
2. When temperature increases, the
pressure of a gas (increases).

17. PT Problem
A gas has a pressure at 2.0 atm at 18°C. What will
be the new pressure if the temperature rises to
62°C? (V constant)
T = 18°C
T = 62°C

18. PT Calculation
P1 = 2.0 atm T1 = 18°C + 273 = 291 K
P2 = ? ?
T2 = 62°C + 273 = 335 K
What happens to P when T increases?
P increases (directly related to T)
P2 = P1 x T2
T1
P2 =
2.0 atm x
K =
K
atm

19. Learning Check GL6
Complete with
1) Increases 2) Decreases
3) Does not change
A. Pressure _____, when V decreases
B. When T decreases, V _____.
C. Pressure _____ when V changes from 12.0 L to 24.0 L (constant n
and T)
D. Volume _____when T changes from 15.0 °C to 45.0°C (constant P and
n)

20. Solution GL6
A. Pressure 1) Increases, when V decreases
B. When T decreases, V 2) Decreases
C. Pressure 2) Decreases when V changes
from 12.0 L to 24.0 L (constant n and T)
D. Volume 1) Increases when T changes from 15.0 °C to 45.0°C
(constant P and n)