Chapters 1 & 2 Vocab Flashcards
ebullioscopic constant
ratio of elevation of boiling point of a solvent caused by dissolving a solute to molality of solution
cryoscopic constant
depression in freezing point when one mole of non-volatile solute is dissolved in 1 kg of solvent
Clausius inequality
dS >= dq/T
- determines direction of change in any natural process
bomb calorimeter
- constant volume (∆U = q)
- closed system
- measure heat evolved as sample is completely combusted in a well-insulated sample chamber
differential scanning calorimeter (DSC)
- 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
calorimeter
device that measures heat exchanges during physical & chemical changes
molecular gastronomy
movement that incorporates science and new technologies in the preparation of food
internal energy
∆U = q + w
- state function
- energy contained within the system
hydrophobic molecule
has very low solubility in water
Gibbs free energy
∆G = ∆H - T∆S
- for spontaneous change at constant P & T, dG <= 0
heat of fusion
heat required to melt per amount of solid melted
heat of vaporization
heat required to transform a liquid substance into a gas
hydrogen bond
- 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)
entropy of mixing
increase in total entropy when separate systems are mixed without chemical reaction by the removal of impermeable partition between them
osmotic dehydration
- 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)
water activity
- when less than xAP*, interactions with food molecules are stronger than those in pure water (“bound in food”)
ideal dilute solutions
- 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
phase
homogenous state of aggregation of a system that is uniform in composition and physical state throughout
homogeneous
system that consists of only one phase
electronegative
tendency of an atom to attract a shared pair of electrons towards itself
chemical potential (µ)
- 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)
ultrafiltration / reverse osmosis
- process of forcing water out through a semi-permeable wall or membrane by applying pressure
heterogeneous
system that consists of more than one phase
ultrafiltration
- use semi-permeable membranes with large pore sizes
- separate out colloidal-size particles and larger suspended materials from solvent water
reverse osmosis
- 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
cyroscope
devices used to measure the freezing point of liquids
triple point
- temp and pressure at which all 3 phases can exist in equilibrium
- pressures for water are very low
reverse osmosis
- 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
fouling
blocking of the pore by dispersed particles
moisture sorption isotherms
- 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)
dendrite
- branched crystals
- characteristic of runaway freezing in undercooled water
hard water
water with a high concentration of dissolved minerals salts of calcium and magnesium
freeze concentration
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
freezing point depression
decrease of freezing point of a solvent due to addition of a non-volatile solute
sorption isotherm hysteresis
desorption give higher equilibrium moisture contents than absorption (food adsorbs a smaller amount of water)
