go to the AUS-e-TUTE homepage
home test exam game contact
 

 

Charles' Law

Key Concepts

  • At constant pressure, the volume of a given quantity of gas is directly proportional to the absolute temperature : V T (in Kelvin)

    So at constant pressure, if the temperature (K) is doubled, the volume of gas is also doubled.

    OR

    At constant pressure for a given quantity of gas, the ratio of its volume and the absolute temperature is a constant : V/T = constant, V/T = k

  • At constant pressure for a given quantity of gas : Vi/Ti = Vf/Tf

    where Vi is the initial (original) volume, Ti is its initial (original) temperature (in Kelvin), Vf is its final volme, Tf is its final tempeature (in Kelvin)

    Vi and Vf must be in the same units of measurement (eg, both in litres), Ti and Tf must be in Kelvin NOT celsius.

    temperature in kelvin = temperature in celsius + 273 (approximately)

  • All gases approximate Charles' Law at high temperatures and low pressures.

    A hypothetical gas which obeys Charles' Law at all temperatures and pressures is called an Ideal Gas.

    A Real Gas is one which approaches Charles' Law as the temperature is raised or the pressure lowered.

    As a Real Gas is cooled at constant pressure from a point well above its condensation point, its volume begins to increase linearly.
    As the temperature approaches the gases condensation point, the line begins to curve (usually downward) so there is a marked deviation from Ideal Gas behaviour close to the condensation point.
    Once the gas condenses to a liquid it is no longer a gas and so does not obey Charles' Law at all.
    Absolute zero (0K, -273oC approximately) is the temperature at which the volume of a gas would become zero if it did not condense and if it behaved ideally down to that temperature.

Graphical Representations

Expansion of Hydrogen gas at constant pressure

Volume
(mL)
Temperature
(oC)
Temperature
(K)
V/T (K) Graph
25 -23 250 0.1
30 27 300 0.1
35 77 350 0.1
40 127.5 400.5 0.1
45 177 450 0.1

Calculations : Vi/Ti = Vf/Tf

  1. A sample of gas at 101.3kPa had a volume of 1.2L at 100oC. What would its volume be at 0oC at the same pressure?

    Vi = 1.2L                                   Vf = ?

    Ti = 100oC = 100 + 273 = 373K     Tf = 0oC = 0 + 273 =273K

    1.2/373 = Vf/273

    3.22 x 10-3 = Vf/273

    Vf = 3.22 x 10-3 x 273 = 0.88L (880mL)

  2. A balloon had a volume of 75L at 25oC. To what does the temperature need to raised in order for the balloon to have a volume of 100L at the same pressure?

    Vi = 75L                                 Vf = 100L

    Ti = 25oC = 25 + 273 = 298K     Tf = ? (K)

    Vi/Ti = Vf/Tf

    75/298 = 100/Tf

    0.2517 = 100/Tf

    Tf = 100/0.2517 = 397K (397-273 = 124oC)

advertise on the AUS-e-TUTE website and newsletters
 

Search this Site

You can search this site using a key term or a concept to find tutorials, tests, exams and learning activities (games).
 

Become an AUS-e-TUTE Member

AUS-e-TUTE members have access to the Test Centre which contains learning activities (games), tests and exams with worked solutions.

Find out more about AUS-e-TUTE membership.

Become an AUS-e-TUTE member.

 

Register for your Free Newsletter

AUS-e-NEWS quarterly newsletter
 

Ask Chris, the Chemist, a Question

The quickest way to find the definition of a term is to ask Chris, the AUS-e-TUTE Chemist.

Chris can also send you to the relevant
AUS-e-TUTE tutorial topic page.

 

Practice

Calculate the final volume of a gas using Charles' Law
Enter initial volume of gas: L
Enter initial temperature of gas: K
Enter final temperature of gas: K
Click Calculate:
Calculation:
Final Volume of gas = L
To start again, click Reset:
 

Related AUS-e-TUTE Topics

Gay-Lussac's Law of Combining Gas Volumes

Boyle's Law (Mariotte's Law)

Ideal Gas Law

 

Bookmark AUS-e-TUTE

  Bookmark this site!
 
© AUS-e-TUTE