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Energy:Matter in Motion

Chapter 5

Remind Ms J to clock in

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

Energy:

• the ability to do work

Why do food scientists care?• They examine how heat is transferred

during cooking and preservation and how energy affects the structure of food during such processes– This helps develop new food products to

meet the needs of consumers


Potential and Kinetic EnergyPotential energy:is stored energy. In food it is in the form of chemical potential energy called calories• Food contains internal potential

energykinetic energy:energy of motion. The faster an object moves, the more kinetic energy it has

continued


Forms of Energy

All forms of energy are used by the food industry:

– Mechanical (potential plus kinetic)– chemical– electrical– nuclear– Radiant

Energy can change from one form to another

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Forms of Energy and Food

• Mixers, blenders, and food processors convert electrical energy to mechanical energy that performs work on food

• Metabolism allows the body to utilize chemical energy from food when bonds between atoms that make food are broken

• Electrical energy is converted into mechanical or radiant energy for food processing


Forms of Energy and Food

• cooking appliances and outdoor grills use radiant energy to cook food

• Microwave ovens convert electrical energy to radiant energy (low-frequency electromagnetic waves called microwaves)

• Nuclear energy is used in food preservation such as irradiation

continued


Measuring Energy

Heat:is an energy transfer from one body to another caused by a temperature difference between the 2 bodies• Food energy is measured in terms of

the capacity to produce heatcalorie:heat needed to raise the temperature of one gram of water one degree Celsius continued


Measuring Energy

Heat capacity: ability of a substance to absorb heat (high water content, high capacity)Specific heat:amount of energy needed to raise the temperature of 1 g of a substance 1° CelsiusTemperature:measure of the average kinetic energy of molecules Very important to ensure food safety and product quality

continued


How Heat is Transferred

• Heat flows from hot objects to cooler ones

• Thermodynamics studies heat flow and temperature in relation to material properties

continued


Conduction:

• the transfer of heat through matter from particle to particle collisions

• Occurs only in metals at the molecular level

• Heated electrons skip over tens or hundreds of atoms and speed the heat transfer

continued©Goodheart-Willcox Publisher


Convection:

• is the transfer of heat by the motion of molecules in fluids, such as water or air– As the temperature increases, convection

currents are generated that speed heating– It is faster than conduction

Ex. cooking food in water

continued©Goodheart-Willcox Publisher


Radiation

• the transfer of heat by electromagnetic waves

– It does not need the presence of matter

– Ex. broiling and rotisserie cooking

– causes most of the browning of baked and roasted foods

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Energy Flow in Phase Changes• Phase changes need a flow of energy

Fusion/melting:solid to liquid phaseCrystallization/freezing:liquid to solid phase is called freezing latent heat of fusion:energy needed to melt or freeze a substance

continued


Energy Flow in Phase ChangesEvaporation/vaporizationliquid to gaseous phase

Condensation/liquefactiongas to a liquid phase

latent heat of vaporizationenergy needed to evaporate or condense a substance is the

continued


Energy Flow in Phase Changes

Deposition– gas phase to a solid phasesublimation– solid phase to a gas phase

At the point of a phase change, the temperature remains constant

continued


Factors That Affect Rates of Reaction in Food Preparation• Temperature of reactants

– The rate of a reaction approximately doubles for every 10°C increase in temperature

• Amount of surface area– The greater the surface area, the faster

the reaction is

• Thickness of the food– The thicker the food, the longer it will

take to cook

images shutterstock.com energy: matter in motion chapter 5 remind ms j to clock in

Documents

electrical energy

forms of energy

energy transfer

mechanical energy

chemical energy

energy of motion

bodies food energy

stored energy