# Relationship between pressure and volume for a sample of air

### How to Calculate Air Volume | Sciencing

At constant temperature of 35 ºC, a sample of gas occupies a volume of L and has a pressure of 2 atm. If the volume of the gas decreased to. In the example of the balloon (above), there is not only gas inside the balloon With density being the ratio of mass per volume, the gas density of the balloon. The gas laws deal with how gases behave with respect to pressure, volume, temperature, and The Gas Laws: Pressure Volume Temperature Relationships.

**Ex: Related Rates - Air Volume and Pressure**

This is called atmospheric pressure. The units of pressure that are used are pascal Pastandard atmosphere atmand torr.

### Boyle's law - Wikipedia

It is normally used as a standard unit of pressure. The SI unit though, is the pascal. For laboratory work the atmosphere is very large.

- The Relationship between Temperature and Volume
- The Relationship between Pressure and Volume
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A more convient unit is the torr. A torr is the same unit as the mmHg millimeter of mercury. It is the pressure that is needed to raise a tube of mercury 1 millimeter. The Pressure-Volume Law Boyle's law or the pressure-volume law states that the volume of a given amount of gas held at constant temperature varies inversely with the applied pressure when the temperature and mass are constant.

Another way to describing it is saying that their products are constant. When volume goes up, pressure goes down. From the equation above, this can be derived: This equation states that the product of the initial volume and pressure is equal to the product of the volume and pressure after a change in one of them under constant temperature.

## Boyle's law

Pressure, Temperature and Volume: The Combined Gas Law Now, what if you have pressure, temperature and volume all together in the same problem? There's a rule for that too.

The Combined Gas Law takes the information from Boyle's Law and Charles' Law and meshes them together to define another aspect of the pressure-temperature-volume relationship. The Combined Gas Law states that the volume of a given amount of gas is proportional to the ratio of its Kelvin temperature and its pressure. That sounds complicated, but take a look at the equation: Again, temperature should be measured in Kelvin.

The law is given by the following equation: In order to get all the units correct, you'll need to convert to SI units, the standard units of measurement within the scientific community. For volume, that's liters; for pressure, atm; and for temperature, Kelvin n, the number of moles, is already in SI units. This law is called the "Ideal" gas law because it assume that the calculations deal with gases that follow the rules.

Under extreme conditions, like extreme hot or cold, some gases may act differently than the Ideal Gas Law would suggest, but in general it's safe to assume that your calculations using the law will be correct.

The upper boundary of the air column that gives rise to atmospheric pressure is the vacuum of space. Being rather light, the mass of a column of air with a 1 cm2 cross section is almost exactly 1 kg.

If a much heavier liquid substance is used to balance this air column, only a relatively small length would be needed. In addition, because the density of liquids does not change with height most liquids are incompressiblesuch an equivalent liquid column has a well defined upper boundary below a vacuumOne of the heaviest liquids at room temperature is mercury Hg and the height of the Hg-column that is equivalent to normal pressure mb is only mm long For this reason, columns of mercury, "hanging" in an inverted vacuum tube, can be used as practical instruments to measure atmospheric pressure see FigureLutgens and Tarbuck, If water were used instead of mercury, the height of the column equivalent to normal pressure would be