Chemistry Formulas

Combined Gas Law Formula

What is Combined Law Formula?

This article deals with the combined gas law formula. The combined gas law combines is a law that combines the three gas laws. Moreover, these three laws are Boyle’s Law, Charles Law, and Gay-Lussac’s Law. So this law is an amalgamation of these three laws that were previously discovered.

Furthermore, this law states that the ratio of the product of volume and pressure and the gas’s absolute temperature is equal to a constant. Most noteworthy, when the addition of Avogadro’s law happens to combined gas law, the ideal gas law results. There is no official discoverer of combined gas law.

Combined Gas Law Formula

Combine gas law is simply a combination of the other gas laws. Moreover, this law works when everything with the exception of volume, pressure, and temperature are held constant. This law makes use of relationships shared by temperature, pressure, and volume.

Understanding the Combined Gas Law

In order to understand the combined gas law properly, imagine that there is a diver and his lungs are full of air when he begins the dive. Furthermore, as he goes deeper underwater, the pressure in the lungs escalates.

When this pressure escalates, the air inside the lungs gets squished. Consequently, the volume decreases. This is where Boyle’s law is in action, which states that the higher the pressure consequently means lower the volume.

Another example can be that of a balloon in the refrigerator.  As the temperature of the balloon in the refrigerator decreases, then consequently the gas volume inside the balloon also decreases.

Also, the balloon reverts to the original size once it is out. Similarly, when temperature increases then consequently there is an increase in volume as well.  This shows Charles law in action.

Take a third example in which a driver is driving down the road. Gradually, the temperature inside the tire increases.  So, as the air expands inside the tire then consequently the pressure also increases. This example represents the Gay-Lussac’s law.

After combining the above three laws, one gets the combined gas law, which shows that:

  • Pressure happens to be inversely proportional to the volume
  • Pressure happens to be directly proportional to temperature
  • Volume is directly proportional to the measure of temperature

Derivation of the Combined Gas Law

The combined gas law is an amalgamation of the three previously known laws which are- Boyle’s law PV = K, Charles law V/T = K, and Gay-Lussac’s law P/T = K. Therefore, the formula of combined gas law is PV/T = K,

Where P = pressure, T = temperature, V = volume, K is constant.

One can adjust the formula for the combined gas law so as to compare two sets of conditions in one substance. In the equation, the figures for temperature (T), pressure (P), and volume (V) with subscripts of one are representative of the initial condition. Also, those with the subscripts of two are representative of the final condition.

P1V1/T1 = P2V2/T2

An important point to note is that the temperature should always be in kelvin for the purpose of calculation. So, if the units are available in the Celsius scale, then one must convert them to kelvin. Furthermore, the conversion to kelvin can easily be done by adding 273 to the particular unit.

Solved Example For You

Question- The initial volume of a gas is 6L and its final volume is 3L. Find out the final pressure of the gas such that the initial temperature is 273 K while the final temperature is 200K. Moreover, 25K Pa is the initial pressure.

Answer- The given parameters are as follows:

P1 = 25 KPa

V1 = 6L

V2 = 3L

T1 = 273K

T2 = 200K

As per the combined gas law

P1V1/T1 = P2V2/T2

So, substituting in the formula:

25 × 6/273 = P2 × 3/200

P2 = 36.626 KPa

Hence, the final pressure of the gas is 36.626 KPa.

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