Under which of the following sets of conditions is a real gas expected to deviate from ideal behaviour? (I) High pressure, small volume (II) High temperature, low pressure (III) Low temperature, high pressure (a) only I (b) only II (c) only III (d) I and III both

Real gases exhibit behaviors that deviate from the ideal gas law under certain conditions. These deviations are due to the fact that real gases have actual volume and the gas particles exert forces on each other.

The ideal gas law assumes that gas particles are point masses with no volume and no intermolecular forces. However, at high pressures, gas particles are compressed close enough that their actual volume cannot be ignored. Moreover, at low temperatures, particles move more slowly, allowing intermolecular forces, like Van der Waals forces, to become significant.

The greatest deviation from ideal behavior typically occurs under conditions of high pressure and low temperature because these conditions enhance the effects of particle volume and intermolecular forces. This real-life behavior of gases is often described using the Van der Waals equation, which corrects the ideal gas law for these factors.

Physical Chemistry is a crucial part of the Joint Entrance Examination (JEE) syllabus, which students aiming for engineering colleges in India need to master. The understanding of gas laws, particularly the distinction between ideal and real gas behavior, is a fundamental topic in this section.

For a competitive exam like JEE, the ability to reason scientifically about the behavior of gases under various conditions is key. When it comes to real gases, students need to comprehend the concept of critical temperature and pressure, as well as the significance of the compressibility factor, a measure of how much a gas deviates from ideal behavior.

In-depth knowledge and practice in calculating and predicting the behavior of gases, using both the ideal gas law and the Van der Waals equation, will give JEE aspirants an edge in tackling physical chemistry questions. Using real-world examples, such as the behavior of gases in car airbags or the refrigeration cycle, can make these abstract concepts more tangible for students.

In contrast to a real gas, an ideal gas perfectly follows the ideal gas law (\( PV=nRT \)), where P is the pressure, V is the volume, n is the number of moles of gas, R is the universal gas constant, and T is the temperature. Ideal gas behavior is a simplification that applies when the interactions between molecules and the volume of the molecules themselves are negligible.

However, such ideal conditions are not always obtainable in the real world. Non-ideal or real gas conditions occur particularly when dealing with high pressure and low temperature - scenarios where these assumptions break down. At high pressures, the particles are forced so closely together that their size becomes an important factor, and at low temperatures, the decreased kinetic energy of the particles amplifies the effects of intermolecular forces.

Understanding the difference between ideal and non-ideal conditions is fundamental in applying the right equations and concepts, not only to solve academic problems but also to accurately describe the behavior of gases in practical applications such as in the chemical and engineering industries.