Publish On: 2019-04-19

Ben joy

Total Post: 542

Question: Describe the fundamental assumptions made in building a model to understand molecular nature of matter

Reply On: 2014-01-15

lala singh

Total Post: 22

ANS: Describe the fundamental assumptions made in building a model to understand molecular nature of matter

In building a model to understand the molecular nature of matter, we start with a set of assumptions. In model building the assumptions made or limits established are consider valid, through they may not seem to be immediately so, if the results predicted are verified by experiment. The fundamental assumptions we make in building this model include the following:
1. We assume that all matter is composed of distinct particles called molecules. In the case of a pure substance, these molecules are alike in all respects. The chemical properties, such as the ability for atoms of various element to combing or interact with one another, are determined by the character of the molecules. The physicals properties depend upon the forces the molecules exert on each other and the relation of these forces to the distance between molecules. Also, the motion of the molecules must be taken into account.
2. In a gas, we assume that the molesters obey Newton’s laws of motion. Except in very special circumstance, we assume that collisions between molecules are perfectly elastic, i.e., that both momentum and kinetic energy are unchanged (for pairs of molecules in collision).
3. It is assumed further that above a certain reference level of internal energy of the body, the molecules are continually in motion. The average speed is dependent upon the temperature, a property which determines the direction of flow of heat energy between an object and its surrounding. When the temperature is constant, the average speed is constant. If one looks at a solid, it is not possible to see the molecules in motion; hence it may be difficult to accept this basis assumption. it is not surprising that we are notable to observe this motion when it is realized that these molecules are going very rapidly, are traveling very short distances, and are revising or changing directions so quickly that any motion would blur out of our vision. For example ,it has been determined that a molecule of hydrogen gas at 0° C has an average speed of 170,0000 cm/s, travels 1.6 × 105 cm between collisions (mean free path) and is involved  in 10 billion (1 × 1010) collisions per second. Similarly, oxygen, which is denser and moves more slowly, still has an average speed at 0° C of 43,000 cm/s, a mean free path of 0.9 × 105 cm and undergoes 4.5 billion (4.5 × 109) collisions per second.

As impossible as it to see this motion, these movements can be amplified to discernible levels by molecular “pumping” which is the basic upon which masers and lasers work.


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