# Thermodynamics: Entropy and the Second Law

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Thermodynamics: Entropy and the Second Law

If you flip a fair coin 8 times, which string of results are you more likely to get? I: HHHHHHHH II: HTHTTHTH String I String II They are equally probable You can’t tell without being given more information. NEXUS/Physics Clicker Questions

If you flip a fair coin 8 times, which string of results are you more likely to get? i: 8 heads ii: 4 heads and 4 tails Result i Result ii They are equally probable You can’t tell without being given more information. NEXUS/Physics Clicker Questions

Suppose we have two blocks of matter touching each other
Suppose we have two blocks of matter touching each other. Suppose each object has 4 DoFs (bins in which to place energy) and we have 4 packets of thermal energy. How many ways are there of distributing all 4 packets to the left object and nothing to the right one? How many ways are there to distribute 2 packets to each object? NEXUS/Physics Clicker Questions

Simple System: A 6 atom gas
How many ways are there to distribute 4 packets of thermal energy “6 choose 4” (6C4) “12 choose 4” (12C4) “18 choose 4” (18C4) Less than “6 choose 4” More than “18 choose 4” Not enough information NEXUS/Physics Clicker Questions

System: Two touching 6 atom gases
There are 4 packets of thermal energy for EACH group of 6 atoms (8 packets total). Compared to a single 6 atom gas, is the number of possible microstates Twice as high Four times as high Eight times as high More than eight times as high Not enough information NEXUS/Physics Clicker Questions

Consider a “joint” system with 6 gas atoms and 6 water molecules
Consider a “joint” system with 6 gas atoms and 6 water molecules. We put in 8 packets of thermal energy They are more likely to be in the gas They are more likely to be in water They are equally likely to be in any atom/molecule NEXUS/Physics Clicker Questions

More thermal energy packets are in the water molecules than in the gas molecules
The water is hotter than the gas The water is colder than the gas The water is at the same temperature as the gas There is not enough information to decide. NEXUS/Physics Clicker Questions

Suppose an isolated box of volume 2V is divided into two equal compartments. An ideal gas occupies half of the container and the other half is empty. When the partition separating the two halves of the box is removed and the system reaches equilibrium again, how does the new internal energy of the gas compare to the internal energy of the original system? The energy increases The energy decreases The energy stays the same There is not enough information to determine the answer NEXUS/Physics Clicker Questions

Suppose an isolated box of volume 2V is divided into two equal compartments. An ideal gas occupies half of the container and the other half is empty. When the partition separating the two halves of the box is removed and the system reaches equilibrium again, how does the new entropy of the gas compare to the entropy of the original system? The entropy increases The entropy decreases The entropy stays the same There is not enough information to determine the answer NEXUS/Physics Clicker Questions

Suppose an isolated box of volume 2V is divided into two equal compartments. An ideal gas occupies half of the container and the other half is empty. When the partition separating the two halves of the box is removed and the system reaches equilibrium again, how does the new pressure of the gas compare to the pressure of the original system? The pressure increases The pressure decreases The pressure stays the same There is not enough information to determine the answer NEXUS/Physics Clicker Questions

A small amount of heat Q flows out of a hot system A (350K) into a cold system B (250K). Which of the following correctly describes the entropy changes that result? (The systems are thermally isolated from the rest of the universe.) |∆SA | > |∆SB| |∆SB | > |∆SA| |∆SA| = |∆SB| It cannot be determined from the information given NEXUS/Physics Clicker Questions

Suppose a small amount of heat Q flows from a system A at low temperature (250K) to a system B at high temperature (350K). Which of the following must be true regarding the entropy of the rest of the universe during this process? It increases by an amount greater than (|∆SA| - |∆SB|) It increases by an amount less than (|∆SA| - |∆SB|) It decreases It stays the same It cannot be determined from the information given NEXUS/Physics Clicker Questions

Suppose a small amount of heat Q flows from a system B at low temperature (250K) to a system A at high temperature (350K). Suppose also that system A and B are isolated from the rest of the universe. Which of the following is true? The scenario described is possible The scenario described will never be seen because of the 1st Law of thermodynamics (conservation of energy) The scenario described will never be seen because of the 2nd Law of thermodynamics (the entropy of an isolated system always increases) The scenario described will never be seen because of both the 1st and 2nd Laws of Thermodynamics

Suppose a small amount of heat Q flows from a system B at low temperature (250K) to a system A at high temperature (350K). Suppose also that system A and B are isolated from the rest of the universe. Which of the following is true? The scenario described is possible The scenario described is highly improbable because of the 1st Law of thermodynamics (conservation of energy) The scenario described is highly improbable because of the 2nd Law of thermodynamics (the entropy of an isolated system always increases) The scenario described is highly improbable because of both the 1st and 2nd Laws of Thermodynamics

A block of ice melts at 00C. The entropy of the resulting water is ____ the entropy of the original block of ice. Greater than Less than The same as NEXUS/Physics Clicker Questions

Temperature-dependent
Consider the decomposition of hydrogen peroxide into water and oxygen:   H2O2(liq) 2H2O (liq) + O2(gas)  ∆S for this reaction under standard temperature and pressure conditions is:   Negative Positive Zero Temperature-dependent NEXUS/Physics Clicker Questions

Which of the following sets of changes are guaranteed to produce a lower G, thereby making a process/reaction more likely to be spontaneous? A negative ∆H and negative ∆S A negative ∆H and positive ∆S A positive ∆H and positive ∆S A positive ∆H and negative ∆S None of the above

A A and C B A and D C B and C D B and D None
Consider the decomposition of hydrogen peroxide into water and oxygen:   H2O2(liq) 2H2O (liq) + O2(gas) The change in enthalpy ∆H for the reaction is kJ/mol.  Consider the following statements.  A. The reaction proceeds spontaneously. B. The reaction does not proceed spontaneously. C. The reaction is exothermic. D. The reaction is endothermic.   Which are true based just on the information given?   A B C D A and C A and D B and C B and D None