# Advice 1: How to find the temperature of the gas

In order to find the absolute temperature of an ideal gas, you can use the equation, which is commonly known as the equation of Clapeyron-Mendeleev. This formula allows to establish the relationship between pressure, temperature of gas and its molar volume.
You will need
• A sheet of paper, a pen.
Instruction
1
The formula is as follows: p•Vm = R•T where p is the pressure, Vm is molar volume of gas, R is the universal gas constant, and T is the absolute temperature of an ideal gas.
2
Find out what data is available to us in order to use the formula, thus: T = (p•Vm)/ R.
3
If we are not aware of molar volume of gas, we can find it by formula:
Vm = V/?. In this formula ? represents the number of substances to Find this value is possible by dividing the mass of gas to its molar mass.
4
The formula, which is called the law of Mendeleev-Clapeyron, is written in this form: p•V = (m/M) • R•T.
5
Modifies this formula to find the temperature of the gas: T = (p•V • M)/(R• m).
6
Find all the values that require us to substitute into the formula. Calculations and find the desired temperature perfect gas.
Note
Carefully examined in the legend, due to a correctly recognized symbol in the formula to prevent the error in the calculations.
The law Mendeleev-Clapeyron also called the combined gas law, that from it are derived the laws of Charles and Gay-Lussac, and Boyle.

# Advice 2 : How to find the temperature at a certain pressure

The temperature of the gas can be found knowing the pressure, using the equation of state for ideal and real gas. In the model of an ideal gas the potential energy of interaction of the gas molecules is neglected, considering it to be small compared to the kinetic energy of the molecules. This model can accurately describe the gas at low pressures and low temperatures. In other cases, consider the real gas model that takes into account intermolecular interactions.
You will need
• The equation of Clapeyron-Mendeleev equation of van der Waals
Instruction
1
Consider first an ideal gas with pressure p, occupies a volume V. the Temperature, pressure and volume of gas connects the equation of state or ideal gas equation of Clapeyron-Mendeleev. It looks like this: pV = (m/m)RT where m is the mass of gas, M is its molar mass, R is the universal gas constant (R ~ 8,31 j/(mol*K). Thus m/M is the amount of substance of gas.
Therefore, the equation of Clapeyron-Mendeleev can also be written as: p(Vm)=RT, where Vm is the molar volume of gas Vm = V/(m/m)= VM/m. Then the gas temperature T can be expressed from this equation: T = p(Vm)/R.
2
If the mass of gas is constant, we can write: (pV)/T = const. From here we can find the temperature changes of the gas when you change other settings. If p = const, V/T = const - the law of Gay-Lussac. If V = const, then p/T = const - the law of Charles.
3
Let us now consider the model of real gas. Equation of state for real gas is called the equation of van der Waals forces. It is written in the form: (p+a*(v^2)/(V^2)) (V/v)-b) = RT. Here, the amendment reflects the strength inthe pull between the molecules, and amendment b - a repulsive force. v - is the amount of substance of gas in moles. The rest of the values correspond to oboznacheniya in the ideal gas equation of state.
Therefore, from the equation of van der Waals the temperature T can be expressed as: T = (p+a*(v^2)/(V^2)) (V/v)-b)/R
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