Advice 1: How to calculate the volume of gas

Gas like substances in other States of aggregation, has a number of parameters, including the volume. The volume of gas is on the basis of other characteristics, which are given in the problem statement. Any gas, regardless of type and composition, has a volume which it is required to find for many tasks.
How to calculate the volume of gas
Gas, whatever its composition, has three main parameters: mass, volume and density. Most tasks operate on the so-called ideal gas, so they must rely only on those given in the values of mass, pressure, temperature. For example, in the problem statement can be specified nitrogen gas N2 with a temperature of 60 degrees, a pressure of 30 kPa and a mass of 0.05 g. Knowing these three parameters and the composition of the gas, by the equation Mendeleev-Clapeyron possible to find its volume. It is necessary to adapt the equation as follows:


By further transformation formulas, find the volume of nitrogen:

V =mRT/pM.

In this case the molar mass M can be found in the table of D. I. Mendeleev. The nitrogen in it is equal to 12 g/mol. Then:

If a known volume under normal conditions, and the amount under other conditions is required, apply the laws of Boyle and Gay-Lussac:


In this case, the transform formula is as follows:


Hence the volume V is equal to:


The index n means the value of a parameter under normal conditions.
If we consider the volume of gas from the point of view of thermodynamics, it is possible to notice that gases can act forces by which changing the volume. The gas pressure constantly, which is typical for Isobaric processes. In such a process the volume changes from one value to another. They may be designated as V1 and V2. In terms of the number of tasks describes some gas under the piston in the vessel. During the expansion of the gas piston moves a distance dl, with the result that the work is carried out:

A=pdV=p(V2 -V1).

This formula relates the change of the gas volume and work. As you know, if given final volume V2, it is possible to find the initial volume V1:

Finally, the easiest way to find the volume of gas on the basis of two different physical parameters - mass and density. If the conditions specified gas with a certain density and mass, its volume should be calculated according to the formula:


Each gas has a specific density, as well as any solid or liquid substance. Therefore, finding the volume of gas in the first place it is necessary to consider this option.

Advice 2: How to find a job gas

The working gas is carried out while changing the volume. That is when the quantity of gas moves the nodes of the heat engine, whether internal combustion engine or a bullet in the barrel of the gun. In various processes of gas is calculated differently.
How to find a job gas
You will need
  • - pressure gauge;
  • thermometer.
If the working gas is carried out in the Isobaric process (at constant pressure), in order to find the working gas using a manometer, measure the pressure of gas. Then measure its volume before executing the operation and after. Find the change in volume of gas, subtracting from the final value to the initial one. Then find the product of the pressure of the gas to change its volume. This will be the work gas at constant pressure A=p•ΔV.
For a perfect gas to calculate work at a constant pressure by applying the equation of Clapeyron-Mendeleev. Find a job gasby multiplying its mass by the number 8,31 (universal gas constant) and the temperature change in operation. The result, divide by the molar mass of gas A=m•R•T/M. in the calculations note that if the work is done by the gas (it expands), then it is positive. If the work is performed on the gas (it is held by outside forces), then the work is negative.
If the work is done by the isothermal expansion (when temperature is constant), find the change in the volume of gas and its temperature. To find the work gas, multiply its mass by the number 8,31 (universal gas constant) and the temperature in carrying out the work. The result, divide by the molar mass of the gas. The number you multiply by the natural logarithm of the ratio of final and initial volumes of gas A=m•R•T•ln(V2/V1)/M.
In General, to find work gas take the integral of a function of pressure by volume. The boundaries of the integral from the initial to the final volume ∫pdV. If there is a schedule of the process gas in the coordinates (V,p), as a rule, it is a straight line, find the area of a trapezium bounded laterally by lines perpendicular to the axis of V the points V1 and V2, bottom axis V, and the top graph of the function. In more complex cases, searched the area of the curvilinear trapezoid.
Useful advice
If volume of gas does not change, the work is not performed.
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