Question

an ideal gas does not exist then why laws were stated?

Answer 1

Brcause Ideal gas is a good approximation to the behavior of many gases under many conditions,

Answer 2

they help us understand and predict the nature of real gasses, even while using newtons laws of motion we take the blocks to be point mass to solve the problem

Answer 3

Because, laws can't be stated for each gas separately.
Ideal gas laws help us predict the properties of all gas in general.

Answer 4

@Hesan laws for ideal gases stated just because at that point of time in the period of
science even the actual composition or structure of gases was even not clearly defined,so
as a remedy for this problem all gases were thought of as ideal and also because concept of gases was a new in the 1800's.

Answer 5

First, because the laws (e.g. equations of state) of an interacting many-body system are generally impossible to derive from first principles, and therefore, when they can be found empirically studying them gives essentially no insight into the underlying physics. That is, there certainly are good empirical equations of state for real gases that give very precise results. Water is a good example: there are "steam tables" that tell you the relationship between pressure, volume, mole number and temperature for steam to great precision at any normal temperature. But studying them gives you zero insight into the underlying physics of water molecules -- because they weren't derived from that physics. By contrast, the ideal gas laws can be easily and transparently derived from underlying physics. To the extent any real sysetm resembles an ideal system, we gain tremendous insight into the underlying physics.

Second, because there exist well-defined mathematical techniques, called perturbation theory generally, which allow you to extend ideal gas results to real systems that differ only slightly from ideality. This not only allows you to calculate useful results, it also gives you good insight into the physics, e.g. the deviations from ideality in certain areas tells you how important certain aspects of the underlying physics are.

Third, which is probably relevant for you although not for working scientists, because teaching them gives the student a solid understanding of how to work with physical law in a simple context, and how the various pieces of chemical physics, including thermodynamics, quantum mechanics, and statistical mechanics in particular, fit together. It's like teaching factoring of polynomials: nobody actually factors polynomials in their day job, as a working mathematician, but knowing how it's done tells you a lot about the structure and nature of algebra -- and that is very useful indeed.

An important fact that may not be as forcefully obvious to you as it is to working scientists is that it is macroscopic behaviour -- what gases do when compressed, expanded, heated -- which is easy to observe. The underlying physics -- what the atoms and molecules are doing, their sizes and shapes and masses, the forces between them -- is generally completely impossible to observe directly. We can only deduce it, painfully, bit by bit, by working backward from patterns in the macroscopic observations. It's like trying to deduce which popular song your friends are listening to on their iPods by watching the expressions on their faces, timing them, et cetera. Very difficult. Very hard to get right, very easy to get wrong.

Consequently, the tools of mathematical physics that allow you to quickly and reliably go from macroscopic observation to microscopic model are prized. The ideal gas equation of state is one of them: if nothing else, as soon as you find a way to define degrees of freedom that obey the ideal gas law, you know you have found a way to divide degrees of freedom into nearly non-interacting sets. That is, itself, a great and useful achievement, because it tremendously simplifies further study.

Answer 6

in simple words we needed some refrence gas to compare nature or behaviour of other gasses. rather than considering a single gas atom they considered as ideal gas to explain many concepts of other gases. . .