Chapters 1 & 2 Vocab

Question 1

ebullioscopic constant

Answer 1

ratio of elevation of boiling point of a solvent caused by dissolving a solute to molality of solution

Question 2

cryoscopic constant

Answer 2

depression in freezing point when one mole of non-volatile solute is dissolved in 1 kg of solvent

Question 3

Clausius inequality

Answer 3

dS >= dq/T

- determines direction of change in any natural process

Question 4

bomb calorimeter

Answer 4

• constant volume (∆U = q)
• closed system
• measure heat evolved as sample is completely combusted in a well-insulated sample chamber

Question 5

differential scanning calorimeter (DSC)

Answer 5

• measures heat exchange as function of temperature
• constant pressure
• open system
• measure heat exchange for each sample necessary to keep them at the same temp

Question 6

calorimeter

Answer 6

device that measures heat exchanges during physical & chemical changes

Question 7

molecular gastronomy

Answer 7

movement that incorporates science and new technologies in the preparation of food

Question 8

internal energy

Answer 8

∆U = q + w

• state function
• energy contained within the system

Question 9

hydrophobic molecule

Answer 9

has very low solubility in water

Question 10

Gibbs free energy

Answer 10

∆G = ∆H - T∆S

- for spontaneous change at constant P & T, dG <= 0

Question 11

heat of fusion

Answer 11

heat required to melt per amount of solid melted

Question 12

heat of vaporization

Answer 12

heat required to transform a liquid substance into a gas

Question 13

hydrogen bond

Answer 13

• strong, attractive, non-covalent interactions between molecules containing hydrogen atoms and other functional groups that contain electronegative atoms
• hydrogen must be bound to strongly electronegative atoms
• very strong, short range, and angle dependent (impose structure)

Question 14

entropy of mixing

Answer 14

increase in total entropy when separate systems are mixed without chemical reaction by the removal of impermeable partition between them

Question 15

osmotic dehydration

Answer 15

• remove internal water from plants (fruits)
• place fruit slices in hypertonic syrup of very concentrated sugar
• water diffuses out into the solution & sugar diffuses in but not that much due to limited permeability of fruit tissues
• maltose is used (no crystallization and no unnecessary sweetness added)

Question 16

water activity

Answer 16

• when less than xAP*, interactions with food molecules are stronger than those in pure water (“bound in food”)

Question 17

ideal dilute solutions

Answer 17

• real solution that is dilute enough for each solute to obey Henry’s Law
• solute molecules are sufficiently separated to make solute-solute interactions negligible
• ex. CO2 in water

Question 18

phase

Answer 18

homogenous state of aggregation of a system that is uniform in composition and physical state throughout

Question 19

homogeneous

Answer 19

system that consists of only one phase

Question 20

electronegative

Answer 20

tendency of an atom to attract a shared pair of electrons towards itself

Question 21

chemical potential (µ)

Answer 21

• partial molar Gibbs free energy
• µ = (∂G/∂n)
• phase that exists at particular temp is the phase with lowest chemical potential (at constant P, also means lowest gibbs free energy & is constant)

Question 22

ultrafiltration / reverse osmosis

Answer 22

• process of forcing water out through a semi-permeable wall or membrane by applying pressure

Question 23

heterogeneous

Answer 23

system that consists of more than one phase

Question 24

ultrafiltration

Answer 24

• use semi-permeable membranes with large pore sizes

- separate out colloidal-size particles and larger suspended materials from solvent water

Question 25

reverse osmosis

Answer 25

• pore size of semi-permeable barrier is on nanometer size
• used to sort out molecules
• allow only water molecules to pass through
• very large applied pressures are needed

Question 26

cyroscope

Answer 26

devices used to measure the freezing point of liquids

Question 27

triple point

Answer 27

• temp and pressure at which all 3 phases can exist in equilibrium
• pressures for water are very low

Question 28

reverse osmosis

Answer 28

• pore size of semi-permeable barrier is on nanometer size
• used to sort out molecules
• allow only water molecules to pass through
• very large applied pressures are needed

Question 29

fouling

Answer 29

blocking of the pore by dispersed particles

Question 30

moisture sorption isotherms

Answer 30

• moisture content vs. activity constant
• amount of water approaches infinity as activity approaches 1 (acts more like pure water, unaffected by other components of the food system)

Question 31

dendrite

Answer 31

• branched crystals

- characteristic of runaway freezing in undercooled water

Question 32

hard water

Answer 32

water with a high concentration of dissolved minerals salts of calcium and magnesium

Question 33

freeze concentration

Answer 33

concentration of a liquid by freezing out ice, leaving a more concentrated solution

• liquid becomes more concentrated as more water molecules are locked up in solid lattice
• ice cannot accommodate substitution

Question 34

freezing point depression

Answer 34

decrease of freezing point of a solvent due to addition of a non-volatile solute

Question 35

sorption isotherm hysteresis

Answer 35

desorption give higher equilibrium moisture contents than absorption (food adsorbs a smaller amount of water)