Chapter 3: The Second Law: The Entropy of the Universe Increases

Question 1

Difference between the first and second law of thermodynamics?

Answer 1

The First Law of Thermodynamics does not tell us whether a particular reaction will spontaneously occur; it just says that whichever way a reaction goes, the energy must be
conserved. The Second Law of Thermodynamics specifies a criterion that predicts the
direction of spontaneous change for a system.
The First Law states that energy is conserved in any process; it may change forms, but the total energy remains constant. However, it doesn’t provide information about the direction of spontaneous changes in a system.

Question 2

What is the second law of thermodynamics?

Answer 2

Second Law of Thermodynamics: The Second Law specifies the direction of spontaneous change in a system. It tells us that natural processes tend to move in a way that increases the entropy of an isolated system. This principle is crucial in understanding how living organisms and other systems maintain stability and control chemical reactions.

Question 3

What is entropy and its sign?

Answer 3

Entropy (S): Entropy is a measure of the disorder or randomness of a system. The Second Law of Thermodynamics states that in an isolated system (one that doesn’t exchange energy or matter with its surroundings), the entropy of the system always increases over time. This means that natural processes tend to lead to greater disorder in an isolated system.

Entropy is an extensive property, dependent on the initial and final states and the amount of the system.
entropy is a state function because it is associated with the spontaneous flow of heat from a hot body to a cooler one.

Question 4

Gibbs free energy?

Answer 4

Gibbs free energy (G) is another thermodynamic variable that combines the concepts of enthalpy (H) and entropy (S). It’s defined as G = H - TS, where H is enthalpy, T is temperature, and S is entropy. The change in Gibbs free energy (ΔG) for a process can be used to determine whether that process will occur spontaneously at constant temperature and pressure. If ΔG is negative, the process is spontaneous, meaning it will happen on its own without external intervention.

Question 5

Background of the Carnot engine

Answer 5

steam engines were widely used but not well understood. Sadi Carnot, in 1824, analyzed an idealized heat engine known as the Carnot engine. This engine operates in a cycle consisting of four reversible steps.Unlike real-world engines, all the steps in the Carnot engine are reversible, meaning they can be run in the reverse direction with no energy loss.

Question 6

what’s the cyclic process of the Carnot engine?

Answer 6

The Carnot cycle involves four steps: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression. These steps are represented in the passage as steps I, II, III, and IV.

calculates the heat (q) and work (w) for each step of the Carnot cycle. It notes that some steps involve heat exchange (q), while others involve work done (w).
Summation of Heat and Work: The total heat absorbed (qcycle) and the total work done (wcycle) by the engine over the entire cycle are calculated. The passage emphasizes that, unlike the change in internal energy (ΔU), neither heat (q) nor work (w) is zero for the cyclic path.

Question 7

purpose of the Carnot cycle

Answer 7

The primary purpose of the Carnot cycle is to establish a theoretical benchmark for the maximum possible efficiency of a heat engine operating between two temperature reservoirs. It provides an upper limit on the efficiency that any real-world heat engine can achieve when extracting work from heat.

Question 8

The efficiency of the Carnot engine is given by the formula:

Answer 8

Efficiency of Heat Engines: The efficiency of a heat engine is a measure of how effectively it converts heat energy into mechanical work. It is typically expressed as the ratio of the work output to the heat input.
Carnot Engine Efficiency: The passage discusses the efficiency of a Carnot engine, which is a theoretical ideal heat engine. The efficiency of the Carnot engine is given by the formula: Efficiency = 1 - (Tcold / Thot),

Question 9

What happens to some of the heat in the engine

Answer 9

In a heat engine like the Carnot engine, not all of the heat absorbed from the hot reservoir can be converted into work. Some of it must be discharged to the cold reservoir. This discharged heat is represented as qcold.

Question 10

Describe the reverse operation of the Carnot cycle?

Answer 10

Reverse Operation: Heat engines can also operate in reverse as refrigerators or heat pumps. In the reverse operation, work is done on the system, and heat is transferred from the cold reservoir to the hot reservoir.

Question 11

Isothermal and Isentropic Processes:

Answer 11

The passage mentions that certain steps in the Carnot cycle (steps II and IV) are isentropic, meaning there is no change in entropy during those steps.

Question 12

spontaneous vs non spontaneous

Answer 12

• A spontaneous change is one that occurs without a
  continuous input of energy from outside the system.
• All chemical processes require energy (activation energy) to
  take place, but once a spontaneous process has begun, no
  further input of energy is needed.
• A nonspontaneous change occurs only if the surroundings
  continuously supply energy to the system.
• If a change is spontaneous in one direction, it will be
  nonspontaneous in the reverse direction

Question 13

is spontaneous change exothermic or endothermic

Answer 13

• A spontaneous change may be exothermic or endothermic.
• Spontaneous exothermic processes include:
  – freezing and condensation at low temperatures
  – combustion reactions
  – oxidation of iron and other metals.
• Spontaneous endothermic processes include:
  – melting and vaporization at higher temperatures,
  – dissolving of most soluble salts.

Question 14

what does not by itself predict the direction of a
spontaneous change.

Answer 14

• The sign of ∆H does not by itself predict the direction of a
  spontaneous change.

Question 15

All spontaneous endothermic processes result in a decrease or increase in
the freedom of motion of the particles in the system?

Answer 15

• All spontaneous endothermic processes result in an increase in
  the freedom of motion of the particles in the system. therefore an increase in entropy
• solid → liquid → gas
• crystalline solid + liquid → ions in solution
• less freedom of particle motion ⇒ more freedom of particle motion
• localized energy of motion ⇒ dispersed energy of motion
• A change in the freedom of motion of particles in a system is a
  key factor affecting the direction of a spontaneous process.

Question 16

The number of microstates (W) in a system is related to the
entropy (S) of the system.
* S = k lnW
* A system with fewer microstates has lower entropy.
* A system with more microstates has higher entropy.
* All spontaneous endothermic processes exhibit an increase in
entropy

Question 17

the sum of the entropy changes of system and surroundings is always?

Answer 17

positive

dS+dS >/0
(systems and surroundings )

if there is a decrease in entropy in a system, there must be an equal or larger increase in entropy in the surroundings

Question 18

What is the 3rd law of thermodynamics?

Answer 18

A perfect crystal has zero entropy at absolute zero

• S sys = 0 at 0 K

ts entropy becomes minimal or zero.

The Third Law helps us understand the concept of entropy in terms of disorder. As a substance gets colder and approaches absolute zero, its particles tend to arrange themselves in a highly ordered, crystalline structure, reducing their overall randomness or disorder. This decrease in disorder is reflected in the decrease in entropy.

A “perfect” crystal has flawless alignment of all its particles.
At absolute zero, the particles have minimum energy, so there
is only one microstate.
* S = k lnW = k ln 1 = 0

Question 19

What does entropy depends on?

Answer 19

Entropy depends on temperature.
– For any substance, S° increases as temperature increases.
* Entropy depends on the physical state of a substance.
– S° increases as the phase changes from solid to liquid to gas.
* The formation of a solution affects entropy.
* Entropy is related to atomic size and molecular
complexity.
– Remember to compare substances in the same physical state