Chapter 4: Thermodynamics

Question 1

Thermodynamics (definition)

Answer 1

the study of the flow of energy in the universe, as that flow relates to work, heat, the different forms of energy, and entropy

Question 2

Zeroth Law of Thermodynamics

Answer 2

Objects are in thermal equilibrium when they are at the same temperature; there is no net exchange of heat energy when objects are in thermal equilibrium with one another

Question 3

Temperature

Answer 3

Related to the average motional (that is, kinetic) energy of the particles

• Heat (energy) flows from hot to cold
• Temperature is a physical property of matter
• SI units = Kelvin

Question 4

Conversion between units of temperature

Answer 4

T(C) = T(K) - 273
T(F) = (9/5)T(C) + 32

Question 5

Absolute zero

Answer 5

the theoretical temperature at which there is no thermal energy (T = 0K)

Question 6

Thermal expansion

Answer 6

The process by which physical properties of matter (length, volume, and even conductivity) change when the matter changes temperature
Thermal expansion = rising temperatures increase length and falling temperatures cause a decrease in length
∆L = (alpha)L∆T

Question 7

Volume expansion

Answer 7

Changes in temperatures cause an increase or decrease in volume
∆V = ßV∆T
ß = 3(alpha)

Question 8

First law of thermodynamics

Answer 8

The change in total internal energy of a system is equal to the amount of energy transferred in the form of heat to the system, minus the amount of energy transferred from the system in the form of work
-Sign convention: work done by the system is positive, work done on the system is negative; heat flow into the system is positive, heat flow out of the system is negative
∆U = Q - W
(∆U is the change in the system’s internal energy)

• Essentially, first law of thermodynamics is that energy is neither created nor destroyed

Question 9

Heat

Answer 9

The process by which a quantity of energy is transferred between two objects as a result of a difference in temperature
- Units: 1 Cal = 10^3 cal = 3.97 Btu = 4184 J

Question 10

Heat transfer: Conduction, convection, and radiation

Answer 10

Conduction: the direct transfer of energy from molecule to molecule through molecular collisions; particles of the hotter matter transfer some of their motional energy to particles of the cooler matter through collisions between the particles of the two matter
Convection: transfer of heat by the physical motion of the heated material; only fluids; heated portions of the fluid rise from the heat source while colder portions sink
Radiation: the transfer of energy by electromagnetic waves; can travel through a vacuum

Question 11

Specific heat

Answer 11

Relationship between heat and temperature for a substance
- specific heat of a substance is the amount of heat energy required to raise 1 kg of a substance by 1ºC or 1K; specific heat of a substance changes according to its phase
Q = mc∆T = mc[T(f) - T(i)]

Question 12

Heat of transformation

Answer 12

• phase changes at constant temperature
• phase changes are related to changes in potential energy, kinetic energy remains constant during phase changes
  Q = mL
  L = heat of transformation of a substance
  - heat of fusion: heat of transformation for phase change from liquid to solid or solid to liquid
  - heat of vaporization: heat of transformation for phase change from liquid to gas or gas to liquid

Question 13

Phase changes to remember

• sublimation
• deposition
• fusion
• freezing
• condensation
• vaporization

Answer 13

• Sublimation = solid to gas
• Deposition = gas to solid
• Fusion = solid to liquid
• Freezing = liquid to solid
• Condensation = gas to liquid
• Vaporization = liquid to gas

Question 14

Work as it relates to thermodynamics

Answer 14

• During any thermodynamic process, a system goes from some initial equilibrium state with an initial pressure, temperature, and volume to some other equilibrium state, which may be at a different final pressure, temperature, or volume
• Sign convention
  
  • gas expands, work done by gas, work is positive
  • gas compressed, work done on gas, work is negative
• when pressure is constant: W = P∆V
• if pressure is not constant, W = area under the curve on a Pressure vs. Volume graph

Question 15

Special cases of the first law of thermodynamics (adiabatic, constant volume, closed cycle)

Answer 15

• Adiabatic (no heat exchange; Q = 0), first law becomes ∆U = -W
• Isovolumetric (constant temperature, isochoric; W = 0), first law becomes ∆U = Q
• Closed cycle (isothermal; ∆U = 0), first law becomes Q = W

Question 16

The second law of thermodynamics

Answer 16

• Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so

Question 17

Entropy

Answer 17

the measure of the spontaneous dispersal of energy at a specific temperature; how much energy is spread out or how widely spread out the energy becomes in a process
∆S = Q/T
- when energy is distributed into a system at a given temperature, its entropy increases; when energy is distributed out of a system at a given temperature, its entropy decreases
* Energy will spontaneously disperse*