Chapter 5: Energy: Matter in Motion Flashcards
Define energy.
The ability to do work.
What are 2 things that food scientists examine relating to energy?
- How heat is transferred during cooking and preservation
- How energy affects the structure of food during such processes
Define potential energy.
Stored energy; the work done in lifting objects to a position
What form is Ep in food?
Chemical potential energy (calories)
Define kinetic energy.
Energy of motion
How does Ek relate to food?
Atoms and molecules always in motion
ex: heat water, atoms move faster, Ek increases
Compare internal vs. external energy.
External: E applied to an object by another source
Internal: E contained in an in an object
What kind of energy does food contain?
Internal potential energy
Name the 5 forms of energy in the food industry.
1) Mechanical
2) Electrical
3) Radiant
4) Nuclear
5) Chemical
Define mechanical energy.
Total kinetic and potential energy of a system.
How does the body use mechanical energy?
When it moves
How does the food industry use mechanical energy?
Food processing, for its equipment
ex: mixers, blenders, and food processors convert electrical energy to mechanical energy
Define chemical energy.
Generated when bonds are broken/formed during chemical reactions
What is an endothermic reaction?
Absorbs energy and lowers temperature
What is an exothermic reaction?
Releases energy and increases temperature
How does metabolism allow us to utilize chemical energy?
Breaks down food –> release chemical energy
Define electrical energy.
Produced by the movement of electrons.
During food processing, what is electric energy converted to?
Mechanical or radiant
What is electrical energy transported by?
Transported through materials that are good conductors (copper, silver, etc.)
Define radiant energy.
Energy transmitted in the form of waves through space or some medium
What is another word for radiant energy?
Electromagnetic spectrum
Name some examples of radiant energy.
Radio waves, ultraviolet waves, microwaves, electric coils, charcoal grills, gas flames, induction cooktops
What forms of energy do microwave ovens convert?
Electrical energy to radiant energy
How do microwaves work?
Electron tube converts electrical E into waves of radiant energy (microwaves). Then, the interior surfaces reflects microwaves towards the food which heats it up.
Name 3 issues with microwaves.
- Food-borne outbreaks (ex: raw poultry)
- Food not cooked properly
- Carry-over cooking (food still being cooked after microwaving)
How does induction cooking work?
Alternating currents –> magnetic field excites electrons -> electric current -> causes flat pan to heat
Why do induction cooktops produce less energy waste?
Since they directly heat the cooking vessel
What type of vessel needs to be used for induction cooking?
Ferromagnetic
Define nuclear energy.
Result of splitting or combining atoms of certain elements, which then give off radiation
How is nuclear energy used in medicine?
X-Rays
How is nuclear energy used in food preservation?
Irradiation
Is irradiation effective? Why don’t we use it often?
One of the most effective, but public thinks food will be radioactive
Define heat.
Heat is an energy transfer from one body to another caused by a temperature difference between the 2.
Define a calorie.
One calorie is the heat needed to raise the temp of one gram of water one oC.
Define a kilocalorie. Why do we use kilocalories?
One kilocalorie is the heat needed to raise the temp of one kilogram of water one oC.
It simplifies calorie count
Define heat capacity.
The ability of a substance to absorb heat
What foods have high heat capacity?
Foods with high water content
Define specific heat.
The ability of a substance to absorb or transfer heat compared to water’s ability.
The amount of energy needed to raise the temperature of 1g of that substance 1oC.
Why is it important to know specific heat?
Helps predict how the food will react during processing
Define temperature.
The measure of the average kinetic energy of a group of individual molecules.
Temperature is an indirect measure of what?
Molecular motion
What is temperature measured with?
Thermometer
Why is it important to measure the temperature of food?
To ensure food safety and product quality
How does heat flow?
Hot objects –> cold objects
What does thermodynamics study?
Studies heat flow and T in relation to material properties
Name the 3 types of heat transfers.
1) Conduction
2) Convection
3) Radiation
Define conduction.
Transfer of heat through matter from particle to particle collisions
Where does conduction occur?
Only in metals at the molecular level
What happens to electrons during conduction?
Heated electrons skip over tens of hundreds of atoms and speed the heat transfer
Define convection.
Transfer of heat by the motion of molecules within a liquid or a gas (water or air)
Is conduction or convection faster?
Convection
Give a common example of convection.
Cooking food in water
Define radiation.
Transfer of heat by electromagnetic waves (browning).
What doesn’t radiation need?
The presence of matter
Give examples of radiation.
Browning of baked goods, roasted foods, broiling, rotisserie cooking, solar oven
What do phase changes need?
A flow of energy
Gas to Solid
Deposition
Solid to Gas
Sublimation
Liquid to Gas
Evaporation
Gas to Liquid
Condensation
Solid to Liquid
Fusion
Liquid to Solid
Crystallization
What is the energy needed to melt/freeze called?
Latent heat of fusion
What is the energy needed to evaporate/condense called?
Latent heat of vaporization
What is the energy needed to complete rearranging of molecules during phase change called?
Latent heat
How is the temperature at the point of a phase change?
T remains constant
Why is understanding phase changes important?
Important in processing and preserving food products
Name the 3 factors that affect rates of reaction in food preparation.
1) Temperature of reactants
2) Amount of surface area
3) Thickness of food
If a child is swinging, the fastest speed will be at the bottom of the swinging motion when maximum ____ is reached and slowest speed at the top of the swinging motion when maximum ___ is reached.
Ek
Ep
If you are sitting perfectly still, your body has _____ energy.
If a friend pulls you out of your chair, your body has ____
External potential energy
External kinetic energy
Where is the internal kinetic energy in your body? Internal potential energy?
Kinetic: molecules within body are moving and doing work
Potential: fat stored as fuel for work
A waterwheel is a form of ____ energy
Kinetic mechanical energy
Making homemade ice cream by mixing salt and ice is a ____ reaction
endothermic reaction, lowers temperature
Digestion is an _____ reaction
exothermic
Dissolving NaOH in water is an ____ reaction
exothermic
What is visible radiant energy called?
Light
How do microwaves cook food?
Microwaves cause polar compounds to vibrate. This causes friction which produces heat.
What kinds of foods will cook faster in a microwave?
Foods with high water content, or foods that are high in fats and sugar (help conduct heat)
What are the advantages of induction cooktops?
- Can boil water in half the time of gas and electric stoves
- Surface of the cooktop stays relatively cool
Why is grilling not seen as healthy?
Carcinogens are formed when meats are grilled
Why is water a great cooking medium?
High heat capacity, rapidly absorb heat or transfer it
Would a glass of water and a pitcher have the same heat? And temperature?
Temp: same
Heat: different because different masses
–> measure of all the kinetic energy
When temperature is the same between two objects, how does heat flow?
It stops
What type of heat transfer is a pan touching a heat source? When will the heat transfer stop?
Conduction
When heat source, pan, and food have the same temp
What type of heat transfer is cooking food in water or baking? When will the heat transfer stop?
Convection
When the fluid is the same temperature throughout
Frost forming on a window in a cold morning is an example of what phase change?
Deposition
Water vapor –> solid state
Gas rising from dry ice is an example of what phase change?
Sublimation
What phase change is used to freeze and dry foods at the same time? ex: freeze dried coffee
Sublimation
If a substance is being cooled, latent heat is being ______. This occurs during ______
released
crystallization, condensation, deposition
If a substance is being heated, latent heat is being ______. This occurs during ______
absorbed
melting, vaporization, sublimation
T or F: The rate of a reaction approximately doubles for every 10oC increase in temperature
True
