Question.1: What are Amagat’s curves?

What decision can be taken from this curve?

Ans.: Amagat’s curve: In 1880, French scientist Amagat and other measured the volume of gases at constant temperature and at different pressures and plotted PV against P in a graph (Fig.6). He observed some lines which deviated from Ideal behavior (dotted straight lines). He got two different types of lines. These lines are called Amagat’s curve.

It was observed that at room temperature the curve for hydrogen and helium show steady rise in the value of PV as P increases. For other gases like O2, N2, CO2 etc. the line first goes down and then rise for higher value of ‘P’. From this curve, it is proved that gases don’t follow the gas laws perfectly. They deviate from ideal nature. But if the temperature is too high they behave as ideal gas. This means that the deviation from ideal behavior become less and less with increase in temperature. So, the gases which don’t obey gas laws perfectly are called real gases.

Question.2: Write down causes of deviation of real gases from ideal behavior.

Ans.: There are two causes of deviation of real gases from ideal nature. They are stated below

(i) Volume defect

(ii) Pressure defect

i) Volume defect: One of the postulates of kinetic theory of gases is that the volume of gas molecules is negligible compared to the volume of the container. But practically, it is not true. Because, at low temperature and high pressure gases can liquefy or solidify. These liquids & solids have certain volume, which is not negligible. Therefore, the gas equation (PV=nRT) deduced for real gases omitting their own volume can not be obeyed by them. In the equation if the volume of the ideal gas is ‘V’ then the volume of the real gas will be (V – nb).

Here, b = Vander Waal’s constant

n = number of molecules

nb = volume of total molecule.

We know that the molar volume of any gas at STP is 22.4 litre.

Question.3: Write down the differences between Ideal gas and Real gas. 

Ans.: The differences between Ideal gas and Real gas as follow: 

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