Exam 1: Energy Transfer and States of Matter

Question 1

how food scientists measure energy

Answer 1

calorie: approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.

Question 2

what happens during: conduction

example

Answer 2

the process by which heat is directly transmitted through a substance when there is a difference of temperature between adjoining regions, without movement of the material.
• waves

Question 3

what happens during: convection

example

Answer 3

the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.

stirring (forced convection), whipping, fan

Question 4

what happens during: radiation

example

Answer 4

the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles that cause ionization.
• the energy transmitted by radiation, as heat, light, electricity, etc.

Question 5

what happens during: microwave cooking

example

Answer 5

magnetrons emit electromagnetic waves
5-7cm = ~1 1/2”
heat of outer edge = conduction = heat at the center

lasagna

Question 6

energy req for phase changes (latent heat of fusion - 80cal/g & latent heat of evaporation - 540cal/g)

Answer 6

d

Question 7

boiling point elevations

Answer 7

bp 100C @ sea level

elevation inc => bp dec as atms pressure dec
960 ft -> -1C
water boils at a lower temp => takes lower to bake/boil

adding solute inc bp
1 mole solute/L solution (add salt) => bp inc 0.52C

Question 8

freezing point depressions (effects of dissolved solutes on freezing points)

Answer 8

h

Question 9

equation for concerting from F -> C

Answer 9

Tc = 5/9 ( Tf - 32)
Tf = Tc x 9/5 + 32

Question 10

4 physical aspects important in food prepartion

Answer 10

(1) heating
(2) measurements
(3) physical state
(4) mixing

Question 11

why heat food?

Answer 11

food safety

cook

Question 12

2 types of heat methods:

Answer 12

(1) dry (air)

2) most (wet, h20/steam

Question 13

examples of dry (air) heat

Answer 13

metal
clay
rocks
stone boiling
charcoal (radiation)
oil / fat

Question 14

examples moist (wet: H20/steam) heat

Answer 14

broth
braising
poaching
boiling
simmering

Question 15

kinetic energy

Answer 15

potential energy w/in the system
heat req for movement
stirring
     -whipping, creaming, beating
          =all generate energy in food systems