Question 1

Which of the following best describes a reversible process in thermodynamics?

Accepted Answer

A process that can be reversed by infinitesimal changes in external conditions, with the system always remaining in equilibrium.

Question 2

A block of ice at $$0^\circ \mathrm{C} is $$placed in a metal box at $$0^\circ \mathrm{C}. $$What is true about the melting process?

Accepted Answer

The ice can melt reversibly if the temperature of the box is changed infinitesimally.

Question 3

Which of the following is an example of an irreversible process?

Accepted Answer

Suddenly increasing the external pressure on a gas from 1 atm to 2 atm.

Question 4

Why can't all the heat absorbed from a hot reservoir be converted into work in a cyclic heat engine?

Accepted Answer

Because the Second Law of Thermodynamics requires that some heat must be expelled to a cold reservoir.

Question 5

Which statement is a correct formulation of the Second Law of Thermodynamics according to Kelvin?

Accepted Answer

It is impossible for any system to absorb heat from a reservoir at a single temperature and convert it completely into work, ending in its original state.

Question 6

A refrigerator removes heat $$|Q_C|$$ from its interior at temperature $$T_C$$ and expels heat $$|Q_H| to $$the room at temperature $$T_H. $$What additional input is required for this process to occur?

Accepted Answer

Mechanical work $$W$$ must be supplied to the refrigerator.

Question 7

The coefficient of performance $$K$$ for a refrigerator is defined as:

Accepted Answer

$$K = \frac{|Q_C|}{|W|}$$

Question 8

Which of the following best explains why heat flows from hot lava into cooler water (as seen in the image of lava entering the ocean)?

Accepted Answer

Because the Second Law of Thermodynamics dictates that heat flows spontaneously from hot to cold.

Question 9

A heat engine absorbs $$Q_H = 500\ \mathrm{J}$$ from a hot reservoir and expels $$Q_C = 300\ \mathrm{J} to a $$cold reservoir in each cycle. What is the thermal efficiency $$e of $$the engine?

Accepted Answer

$$e = \frac{Q_H - Q_C}{Q_H} = \frac{500 - 300}{500} = 0.40$$

Question 10

If a workless refrigerator (one that transfers heat from cold to hot without work input) were possible, what would be the consequence?

Accepted Answer

It would allow the construction of a 100% efficient heat engine, violating the Second Law.

Question 11

Which of the following is NOT a requirement for a process to be considered reversible?

Accepted Answer

There must be a finite temperature difference between the system and surroundings.

Question 12

A car engine is an example of which type of thermodynamic device?

Accepted Answer

A heat engine, converting heat from fuel combustion into mechanical work.

Question 13

Which of the following statements about the First Law of Thermodynamics is correct?

Accepted Answer

It is only concerned with energy bookkeeping and does not determine process direction.

Question 14

In the context of a heat engine, what is a 'reservoir'?

Accepted Answer

A body so large that its temperature remains constant when it exchanges heat.

Question 15

Which of the following is a correct statement of the Clausius formulation of the Second Law of Thermodynamics?

Accepted Answer

It is impossible for any process to have as its sole result the transfer of heat from a cooler to a hotter body.

Question 16

A gas expands freely into a vacuum. This process is:

Accepted Answer

Irreversible, because the process cannot be reversed by infinitesimal changes.

Question 17

Which of the following best describes the efficiency $$e of a $$heat engine?

Accepted Answer

$$e = \frac{	ext{work output}}{	ext{heat input}}$$

Question 18

Which of the following scenarios would violate the Second Law of Thermodynamics?

Accepted Answer

A device that extracts heat from the cold ocean and converts it entirely into useful work.

The Second Law of Thermodynamics: Direction, Efficiency, and Thermal Machines

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