Question

Suppose you had 10 identical molecules enclosed by a box. At a given instant, one molecule has an energy of 100 Joules, and the others are all stationary
(A) What is the average kinetic energy of the 10 molecules?
(B) Is this a situation of high or low entropy?
(C) What happens to the energy and entropy of the molecules in the box as time passes? Does your answer depend on the insulation of the box?

Answer 1

Answer:

A)   K_average = 1/20 m v², B) low entropy , C) entropy increases.

Explanation:

A) The kinetic energy of each molecule

         K = ½ m v²

The average kinetic energy is the sum of each kinetic energy among the number of them

        K_average = (½ m v² + 0 + 0 +) 10

        K_average = 1/20 m v²

B) Entropy is the sum of the states of each molecule, in this configuration there are only two states one with energy and the other with zero energy, so it is a system with low entropy.

       S = k ln W

  Where S is the entropy, k the Bolztmann constant, W the amount of state present in the system in this case is 2

C) Let's start by analyzing the entropy, as time goes by the molecule that is moving collides with the other molecules and transfers them some energy, so the other molecules move to a different state, after a little In time all the molecules will have the same energy, each one in a different state or volume, so the number of possible state increases to 10, so the entropy increases.

Now let's analyze what happens with the energy of the system, for this case we have two possibilities

- The system is isolated, therefore as it cannot exchange energy with the environment, the total energy remains constant even when the energy of each molecule can fluctuate.

- If the system is not isolated, it can exchange energy with the environment, therefore the total energy changes, depending on the difference in energy between the molecules and the environment