Postulates of the Kinetic Molecular Theory

All gases, under ordinary conditions of temperature and pressure, are made of molecules (including one-atom molecules such as are present in samples of the noble gases). That is, ionic substances do not form gases under conditions prevalent on earth. The molecules of a gas act according to the following postulates  

The molecules exhibit negligible intermolecular attractions or repulsions except when they collide. 

Molecular collisions are elastic, which means that although the molecules transfer energy from one to another, as a whole they do not lose kinetic energy when they collide with one another or with the walls of then-container. 

The molecules occupy a negligible fraction of the volume occupied by the gas as a whole. 

The average kinetic energy of the gas molecules is directly proportional to the absolute temperature of the gas. 

---

Ans. The gas laws work for unbonded atoms as well as for multiatom molecules, and so it is convenient to classify the unbonded atoms as molecules. If these atoms were not classified as molecules, it would be harder to state the postulates of the kinetic molecular theory. For example, postulate 1 would have to be stated "Molecules or unbonded atoms are in constant random motion. ... 

B) Review the postulates of the kinetic molecular theory of gases, which are listed on page 58. 

Kinetic energy is the energy of motion. Gas particles have a lot of kinetic energy and constantly zip about, colliding with one another or with other objects. The picture is complicated, but scientists simplified things by making several assumptions about the behavior of gas pcirticles. These assumptions are called the postulates of the kinetic molecular theory. They apply to a theoretical ideal gas ... 

A. Which postulate of the kinetic molecular theory explains why gases expand to fill their containers ... 

An example of this type of model is the kinetic molecular theory, a simple model that attempts to explain the properties of an ideal gas. This model is based on speculations about the behavior of the individual gas particles (atoms or molecules). The postulates of the kinetic molecular theory can be stated as follows ... 

The fourth postulate of the kinetic molecular theory is that the average kinetic energy of the particles in the gas sample is directly proportional to the temperature in Kelvins. Thus, since (KE)avg °c T, we can write... 

We have seen that the postulates of the kinetic molecular theory, combined with the appropriate physical principles, produce an equation that successfully fits the experimentally observed properties of gases as they approach ideal behavior. Two phenomena involving gases provide further tests of this model. 

Using postulates of the kinetic molecular theory, give a molecular interpretation of Boyle s law, Charles s law, and Dalton s law of partial pressures. 

Until now our discussions have dealt with ideal behavior of gases. By this we mean that the identity of a gas does not affect how it behaves, and the same equations should work equally well for all gases. Under ordinary conditions most real gases do behave ideally their P and V are predicted by the ideal gas laws, so they do obey the postulates of the kinetic-molecular theory. According to the kinetic-molecular model, (1) all but a negligible volume of a gas sample is empty space, and (2) the molecules of ideal gases do not attract one another because they are so far apart relative to their own sizes. 

The final topic will briefly present the postulates of the kinetic-molecular theory of gases that describe the behavior of gases on the molecular level. Let s begin with one of the most important properties of a gas, its pressure. 

Postulates of the Kinetic-Molecular Theory The theory is based on three postulates (assumptions) ... 

Use the postulates of the kinetic molecular theory (KMT) to explain why Boyle s law, Charles s law, Avogadro s law, and Dalton s law of partial pressures hold true for ideal gases. Use the KMT to explain the P versus n (at constant V and T) relationship and the P versus T (at constant V and n) relationship. 

Without consulting your textbook, list and explain the main postulates of the kinetic molecular theory for gases. How do these postulates help us accoimt for the following bulk properties of a gas the pressure of the gas and why the pressure of the gas increases with increased temperature the fact that a gas fills its entire container and the fact that the volirme of a given sample of gas increases as its temperature is increased. 

A gas that obeys all the postulates of the Kinetic Molecular Theory is called an ideal gas. Obviously, no real gas obeys the assumptions made in the second and fourth postulates exactly. But a nonpolar gas at high temperatures and low pressure (concentration) approaches ideal gas beha dor. 

---