18.2.1 Entropy and the Second Law of Thermodynamics

Question 1

Entropy and the Second Law of Thermodynamics

Answer 1

• Spontaneous processes that proceed without a decrease in energy are entropy-driven.
• Entropy changes are driven by statistics.
• The second law of thermodynamics states that, for any spontaneous process, the total entropy of the universe must increase.

Question 2

note

Answer 2

• The majority of spontaneous processes occur because of a decrease in energy. There are some processes, however, that occur spontaneously in spite of a required increase in energy.
• The process of water evaporating is a commonly observed spontaneous process that requires energy to occur. The enthalpy is positive, but it still happens. Such spontaneous processes that proceed with an increase in energy are entropy-driven. Entropy changes are driven by statistics.
• Two glass bulbs are connected with an interconnecting tube containing a stopcock. One of the bulbs contains a molecule of gas. After the valve is opened for a 24-hour period, what is the probability that the gas molecule will still be in the glass bulb on the left? There is a 50% probability, since there is an equal probability that the molecule will be in either one of the two bulbs. As additional molecules are added to the system, the probability of the molecules occurring in the same bulb is (1/2) n . The probability of a large number of molecules
  ending up in the same bulb is infinitesimal. The probability of molecules moving from an area of low concentration into an area of high concentration is extremely small.
• The second law of thermodynamics states that, for any
  spontaneous process, the total entropy of the universe must increase.
• Condensation of water on a cold bottle seems to defy the second law of thermodynamics. However, energy is lost to the surroundings as heat, which increases the entropy of the universe. Even changes in enthalpy can be explained by the drive to increase disorder.

Question 3

Look at the entropy experiment for a gas in two bulbs.

Which statement about this experiment is not correct?

Answer 3

As you add more gas molecules, the probability of finding them all on one side at any time increases

Question 4

Suppose that, instead of having two connected bulbs, you have three connected bulbs. Assume that you start with the valve closed, add some gas molecules to one bulb, and then remove the valve. Which of the following shows the correct expression for the probability of finding all the gas molecules in one container after 1 hour?

Answer 4

probability = (1/3)^x, where x = the number of molecules

Question 5

Which of the following statements is not correct?

Answer 5

Nature will spontaneously transfer heat between two areas at equal temperatures (and pressures).

Question 6

Look at the thermal energy drawing.

Which statement about this thermal energy event is not correct?

Answer 6

Heat moving into the house would violate the first law of thermodynamics.

Question 7

Look at the entropy experiment.

Assume that we start with the valve closed, add one (or more) gas molecules to one side, and then open the valve. Which statement about this experiment is not correct?

Answer 7

If you place two gas molecules in the left bulb and then open the valve, the chance of finding both molecules on the right side one hour later is 75%.

Question 8

Which statement about enthalpy is not correct?

Answer 8

In a spontaneous reaction, the enthalpy change is always positive.

Question 9

Which statement about entropy is not correct?

Answer 9

A spontaneous event can sometimes cause a decrease in the entropy of the universe.

Question 10

Which statement about the evaporation of water is not correct?

Answer 10

The product of the evaporation event is at a lower energy level.

Question 11

Which statement is not correct?

Answer 11

If there is a decrease in the energy of the system, the reaction is spontaneous.

Question 12

Which statement about spontaneous processes is correct?

Answer 12

The majority of spontaneous processes occur with a release of energy.