Midterm 1 Lecture Review

Question 1

Intensive Properties

Answer 1

Normalized by mass or moles of the substance and are thus intrinsic to the substance of interest under these conditions. Units: J/g, kJ/mol, BTU/lb, m^3/kg, lit/mol

Question 2

Thermal Radiation

Answer 2

transfer of heat through electromagnetic waves > ref. stefan-boltzman law

Question 3

Supercritical Fluid

Answer 3

a substance above its critical point on a P-V diagram where T>Tcr and P>Pcr

Question 4

Relative Humidity

Answer 4

the amount of water vapor in the air (by mole or mass), relative to the amount at saturation (i.e. the maximum amount of H2O the air can hold without condensation) - RH = PH2O / Psat(T)

Question 5

Flow Work

Answer 5

The energy required to move fluid in or out of a control volume > the work done by the fluid to push mass across a system boundary

Question 6

Well depth

Answer 6

The energy required to separate two particles from their most stable configuration. A larger well depth = stronger intermolecular attraction; a smaller well depth = a weaker attraction (reference diagram from class)

Question 7

Convection

Answer 7

transfer of heat from bulk fluid flow > ref Newton’s law of cooling/ convection formula

Question 8

Specific Volume

Answer 8

the volume occupied by a unit mass of a substance, defined as v = V/m (m^3/kg)

Question 9

Freeze Drying

Answer 9

Drying method that avoids crossing the vapor-liquid dome. Freeze-dried materials mostly retain their structure, however, ice crystal growth can disrupt the fine structure of delicate biological specimens (cells, tissues, whole organisms). > used in biotech/pharma industry

Question 10

Mass flow rate

Answer 10

the amount of mass passing through a given surface per unit of time; it is used to quantify the rate at which mass enters or exits the system; influences the overall energy balance of the open system; units: kg/s

Question 11

Power

Answer 11

a rate of doing work (W dot); units: Watt (1 J/s), KW, horsepower

Question 12

Conduction

Answer 12

the transfer of heat through atomic and molecular motion; ref. Fouriers law of conduction

Question 13

Evaporative cooling

Answer 13

A process by whihc a liquid absorbs heat from its surroundings and undergoes phase change into vapor, reducing the temperature of the remaining liquid in the surrouding environment; perspiration in humans, cooling towers, in power plants, & desert climated adaptations

Question 14

Saturated Vapor

Answer 14

at a condition where vapor can coexist/ be in equilibrium with its corresponding liquid phase

Question 15

Critical point drying

Answer 15

aka supercritical drying; uses CO2 with its critical point at 31.1C & 73.9 bar; removes liquid from a material without surface tension effect by transitioning the liquid to a supercritical state and then depressurizing it into a gas; prevents structural collapse making it ideal for delicate samples like biological samples and aerogels

Question 16

Adiabatic

Answer 16

No heat is transferred to or from a system, meaning that all energy changes are due to work done on or by the system; Q = 0 so dU = -W; adiabatic process describes a condition where Q = 0 during a specific thermodynamic change

Question 17

Vapor pressure

Answer 17

think of as a liquid property; the pressure the molecules exert as they randomly try to leave the liquid phase

Question 18

Dew Point (temperature)

Answer 18

the temperature at which air that is cooled becomes saturated (and thus any incremental further drops in temp will cause the first liquid droplets to condense out)

Question 19

The mechanical equivalence of heat

Answer 19

the principle that heat and mechanical work and interchangeable forms of energy; i.e. a specific amount of work produces an equivalent amount of heat; ref. first law of thermodynamics > dU = Q - W

Question 20

Isothermal

Answer 20

a process that occurs at a constant temp (dT = 0); any heat added or removed from the system is fully converted into work or internal energy changes; common in ideal gas behaviour and phase changes

Question 21

Open system

Answer 21

a system that exchanges mass and energy (heat and work) with its surroundings; turbines, pumps, boilers, etc.

Question 22

Steady State

Answer 22

energy inside the system is not changing; any heat or mass flows in or out are at constant rates; all time derivatives are set to zero

Question 23

Collision diameter

Answer 23

the separation distance between two particles at which Uintermolecular is zero in the pair potential function; indicated the point where attractive and repulsive forces balance before repulsion dominated at shorter distances

Question 24

Emissivity

Answer 24

a surface property that quantifies how efficiently a surface emits thermal energy; 0<E<1; 1: “black body”, a perfect emitter or absorber; 0: no emission, perfect reflector

Question 25

Shaft work

Answer 25

the mechanical work transmitted by a rotation shaft; turbines, compressors, pumps, etc.

Question 26

Closed system

Answer 26

exchanges energy but not mass with it surroundings; not mass transfer across boundaries; heat and work can cross boundaries

Question 27

Transient process

Answer 27

system properties change with time until reaching a steady state

Question 28

Isenthalpic

Answer 28

a systems enthalpy remains constant (dH = 0); other properties like temperature or pressure can change

Question 29

Heat pipes

Answer 29

sealed pipe-like devices that promote heat transfer between their two ends through a trapped "working fluid" that undergoes evaporation.condensation processes

Question 30

Isolated system

Answer 30

no mass nor energy is exchanged with its surroundings; No Q, W, mass entry/exit

Question 31

Internal energy

Answer 31

U; a collection of microscopic modes including molecular translation, rotation, vibration, intermolecular forces, bond energies, microscopic KE and PE; excludes macroscopic energy forms like the KE or PE of the system as a whole

Question 32

Heat transfer coefficient

Answer 32

rate of heat transfer per unit area per unit temperature difference between a surface and a fluid;

Question 33

Vacuum evaporation

Answer 33

the rapid removal of water or other solvents without exposing the product to high temperatures; can damage structure through shrinkage and collapse caused by liquid water surface tension

Question 34

Extensive properties

Answer 34

proportional to the amount (mass or moles) of the substance; Units: J, BTU, m^3

Question 35

Enthalpy

Answer 35

total heat content of a system; H = U + PV

Question 36

Heat flux

Answer 36

rate of heat energy transfer per unit area; quantifies the amount of heat flowing through a surface; Units: W/m^2

Question 37

Enthalpy of formation

Answer 37

the change in enthalpy when one mole of a compound is formed from its elements in their standard states under standard conditions; used to calculated the enthalpy changes in chemical reactions

Question 38

Superheated vapor

Answer 38

rightmost region on PV diagram; vapor that has heated beyond its saturated state (temp is beyond Tsat)

Question 39

Enthalpy of reaction

Answer 39

the change in enthalpy (dH) during a chemical reaction, representing the difference between enthalpies of the products and reactants; indicated whether a reaction absorbs heat (dH>0) or releases heat (dH<0_