Chapter 4: Heat and the Second Law of Thermodynamics

Flashcards cover the key concepts of heat, thermal energy, heat transfer mechanisms, and the three statements of the Second Law of Thermodynamics, as discussed in the lecture notes.

What is meant by Nature having a preferred direction of time?

The thermodynamic arrow of time; processes tend to occur toward increasing entropy and do not spontaneously reverse.

Before the late 1800s, did Newton’s laws prohibit time running backwards?

No; processes were considered equally likely to run in either temporal direction.

Which fundamental law does not depend on time and leads us to study heat?

The First Law of Thermodynamics (Conservation of Energy).

What is thermal energy?

The collective kinetic energy of atoms and molecules in a substance, associated with their vibrations; energy content increases with vibration vigor.

How is temperature related to thermal energy?

Temperature is proportional to a measure of an object's total thermal energy.

What is heat?

Heat is the transfer of thermal energy between bodies due to a temperature difference.

What is specific heat capacity?

A measure of how much thermal energy is needed to raise the temperature of a substance by 1°C (per gram, etc.).

What are the specific heat capacities of water and ethyl alcohol?

Water: 4.184 J/g°C; Ethyl alcohol: 2.460 J/g°C.

If the same amount of energy is applied, which heats up faster: water or ethanol, and why?

Ethanol heats up roughly twice as fast because it has a lower specific heat capacity.

What are the three modes of heat transfer?

Conduction, Convection, and Radiation.

What is conduction?

Energy transfer through microscopic collisions between neighboring atoms and molecules.

What is convection?

Heat transferred by bulk motion of a fluid (e.g., rising hot water in a pot).

What is radiation?

Transfer of energy by electromagnetic waves (no medium needed).

Can conduction, convection, and radiation occur together in a real situation?

Yes; they can occur in combination (e.g., Sun heating the ground, air rise, etc.).

What is the relationship between thermal energy and heat?

Heat is the process of transferring thermal energy; thermal energy is the stored energy inside a system.

Which method heats the Earth from the Sun?

Radiation.

In the Sun, what process moves plasma from the center to the surface, producing convection currents?

Convection.

As plasma moves toward the Sun’s surface and cools, by what mechanism does it transfer energy to surrounding atoms by contact?

Conduction.

The Sun sends energy to Earth in the form of light rays. What method of heating is this?

Radiation.

What does Second Law Statement 1 say about heat flow between a cool body and a hot body?

Heat will not flow spontaneously from a cool body to a hot body; temperatures tend to equalize when in thermal contact.

What does Second Law Statement 2 say?

No engine can convert heat completely into useful work; some energy is always lost to the environment, so efficiency < 100%.

Can you give an everyday example of Second Law Statement 2?

Light bulbs convert some energy to light but most is released as heat to the surroundings; exhaust gases release heat as waste rather than all into work.

What does Second Law Statement 3 say?

Every isolated system becomes more disordered with time (entropy increases).