What is Charles Law – Definition, examples, graph, Charles Gas Law

There are three basic gas laws (Boyle’s, Charles’ and Gay-Lussac’s). But here at the end of the article, You will able to describe What is Charles Law – Definition, examples, graph, Charles Gas Law. Let’s start discussing it one by one.

What is Charles Law – Definition

Charles law states that For a gas, temperature and volume are directly proportional to each other. It should be remembered that this law is applicable only when the number of particles of gas remains the same for a given volume.What is Charles Law - Definition, examples, graph, Charles Gas Law

  • As the temperature of a gas goes up, its volume goes up.
  • As the temperature of a gas goes down, its volume goes down.

Charles Gas Law

Jacques Charles is credited with this Gas Law relating temperature and volume, although he didn’t publish it. He may have been too busy taking rides in hot air balloons. A colleague, Joseph Louis Gay-Lussac, published it and very honorably gave Charles credit.

Charles’s Law says that for a given amount of gas, at a fixed pressure, volume and temperature are directly proportional.

V ∝ T.

You can write this mathematically as

V = kT

  • where V = volume,
  • T = temperature in Kelvin,
  • and k = is a proportionality constant.

We can rearrange this equation so it reads

V/T = k, or The ratio of volume to temperature is a constant, k.

Very often, Charles’s law is used to compare two situations, a “before” and an “after.”

  • In that case, you can say V /T = k, and V /T = k,
  • so you can write Charles’s law as V /T = V / T.

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Charles Law Examples

If you heat up a gas, it expands – the gas particles move faster, and they take up more space. Following is based on the real-life example that has been performed number of times.

  • It has been seen that a balloon when heated expands. This results in the gas particles bang against the sides. (by expanding, that keeps the pressure constant). The faster the gas particles move, the more they will push on the sides of the balloon, expanding it.
  • If, on the other hand, you cool the gas down – you put your balloon on ice – that slows the particles of gas down, so the balloon will contract.

Example 1

A hot air balloon has a volume of 2,800 m3 at 99 C°. What is the volume if the air cools to 80 C°?
Answer – 

We will use “before and after” form:
V1 /T1= V2/T2

We substitute in what we know – remember to convert temperatures to Kelvin.

  • Kelvin = C° + 273.15.
  • T1= 372.15 Kelvin, T2 = 353.15 Kelvin

V2 = 2657 m3

Example – 2
Here’s another example: At 0 C°, a gas occupies 22.4L. How hot must the gas be, in Celsius, to reach a volume of 25.0 L?

Answer –

V1 /T1= V2/T2.

Convert temperature to Kelvin: Kelvin = C° + 273.15.
T1 = 273.15 K
Substituting in what we know: 22.4L/273.15K = 25.0L/T2
Solve for T2

  • (22.4L) T2 = (273.15 K)(25.0L)
  • T2 = (273.15K) (25.0L)/22.4L
    T2 = 304.9 K

Convert to C°: C° = Kelvin – 273.15
T2 = 31.7 C°

Charles Law Graph Explanation


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