Everything Science Grade 11

CHAPTER 5. THERMAL PROPERTIES AND IDEAL GASES 5.3

DEFINITION: Charles’ Law

The volume of an enclosed sample of gas is directly proportional to itsabsolute tem-

perature provided the pressure is kept constant.

FACT

Charles’s Law is also

known as Gay-Lussac’s

Law. Charles did not

publish his work. Gay-

Lussac later rediscovered

this law and referenced

Charles’s work, but said

that it was only by great

luck that he knew of it

and that his experiment

was different.

General experiment: Charles’s Law

Aim: To demonstrate Charles’s Law using simple materials.

Apparatus: glass bottle (e.g. emptyglass coke bottle), balloon, Bunsen burner, retortstand

Method:

1. Place the balloon over the opening of the empty bottle.


2. Place the bottle on the retort stand over the Bunsen burner and allowit to heat up. Ob-
   serve what happens tothe balloon. WARNING: Be careful when handling the heated
   bottle. You may need towear gloves for protection.

Results: You should see thatthe balloon starts to expand. As the air insidethe bottle is

heated, the pressure also increases, causing thevolume to increase. Since the volume of the

glass bottle can’t increase, the air moves into theballoon, causing it to expand.

Conclusion: The temperature and volume of the gas are directly related to each other. As one

increases, so does the other.

Mathematically, the relationship between temperature and pressure canbe represented as follows:

V∝ T

or

V = kT

If the equation is rearranged, then:

V

T

= k

and, following the samelogic that was used for Boyle’s law:

V 1

T 1

=

V 2

T 2

The equation relating volume and temperature produces a straight line graph (refer back to the notes
on proportionality if thisis unclear). This relationship is shown in Figure5.3.