The gas laws | Statement, Formula, graph of Charles’ law, Boyle’s Law & Pressure law

The gas laws tell us the relationship between pressure, temperature, and volume of gases. The gas laws can be stated in a convenient form for calculations when absolute temperatures are used. The laws we are going to cover here are (1) Charles’ Law (2) Pressure Law, and (3) Boyle’s Law.

Charles’ law | Statement of Charles’ law with explanation

Charles’ law may be stated as follows: The volume of a fixed mass of gas is directly proportional to its absolute temperature if the pressure is kept constant.

We can then say that the volume V is directly proportional to the absolute temperature T, i.e. doubling T doubles V, etc. Therefore
V ∝ T or V = constant × T
or
V/T = constant

Charles’ law Graph from the lab experiment

Let’s have a quick view of Charles’ law Graph to understand the effect of temperature on volume with pressure constant.

The graph does not pass through the Celsius temperature origin (0 ºC). If they are produced backward they cut the temperature axis at about –273 ºC. This temperature is called absolute zero because it is found to be the lowest temperature possible. It is the zero of the absolute or Kelvin scale of temperature. Degrees on this scale are called kelvins and are denoted by K.

Charles’ law Graph from the lab experiment

Pressure Law Statement | explanation

The pressure law may be stated as follows: The pressure of a fixed mass of gas is directly proportional to its absolute temperature if the volume is kept constant.

As per Pressure Law, pressure p is directly proportional to the absolute temperature T
p ∝ T or p = constant × T
or
p/T = constant

Pressure Law Graph

Here is the Pressure law graph.

Boyle’s Law Statement | explanation

Boyle’s law may be stated as follows: The pressure of a fixed mass of gas is inversely proportional to its volume if its temperature is kept constant.

p is inversely proportional to V.
In symbols: p ∝ 1/V
p = constant x (1/V)
pV = constant
If several pairs of readings, p1 and V1, p2 and V2, etc. are taken, then it can be confirmed that p1V1 = p2V2 = constant.

Boyle’s Law graphs

Since p is inversely proportional to V, then p is directly proportional to 1/V. A graph of p against 1/V is, therefore, a straight line through the origin.

Boyle’s Law graphs

Combining the Gas Laws

The three equations can be combined giving the following equation:
pV/T = constant

For cases in which p, V, and T all change from, say, from p1, v1, T1 to p2, v2, T2, then
p1V1 / T1= p2V2/ T2

The gas laws | Statement, Formula, graph of Charles’ law, Boyle’s Law & Pressure law
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