Name: Gay Lussac's and Avogadro's Law
Uploaded: 2019-07-19
Duration: 18 min 33 s
Description: The video beautifully explains the two laws for an easy understanding of the students. Gay Lussac's law and Avogadro's law are explained here. Watch and learn.

Question

Why do real gases show deviation from ideal behaviour ? Write van der Waals equation for

n

moles of a gas.

Accepted Answer

At high pressure or low temperature, real gases show deviation from ideal behaviour. This deviation is based upon kinetic theory of gases. There are two assumptions of kinetic theory of gases which are proved to be wrong at high pressure or low temperature
These two assumptions are:
i) The molecules of gases are considered to be point masses and the volume occupied by these point masses is negligible as compared to the total volume of gas.
ii) The molecules of gases are present at a large distance due to which the force of attraction or repulsion among the gas molecules becomes negligible.

The above assumptions are true only if pressure is low or temperature is high.Only in this condition, the distance among the molecules is large.

But, if decrease the pressure or increase the temperature, the molecules come closer. In such situation, force of attraction or repulsion between the molecules cannot be neglected. Also, the volume occupied by the gas will be so small that the volume occupied by its molecules cannot be neglected.

van der Waals equation for $n$ moles of a gas can be written as given below:
$(P + \frac{{an}^{2}}{V^{2}}) (V - nb) = nRT$
Where, $P$ -pressure of the gas, $V$ -Volume of the gas, $R$ -Gas constant, $T$ -Temperature, $a$ and $b$ -van der Waal’s constants.

Why do real gases show deviation from ideal behaviour ? Write van der Waals equation for $n$ moles of a gas.

Important Questions on States of Matter: Gases and Liquids

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