Food and EnergyThe Basics of Heat

Transfer

The Flow of Energy

Thermochemistry - concerned with heat changes that occur during chemical reactions

Cranking up the Heat: Basic ThermodynamicsEnergy - capacity of an object

to do work or produce heat

Kinetic EnergyThe energy an object has due

to its motion

Potential EnergyStored energyEnergy of position

External EnergyThe energy applied to an object by another source

Internal EnergyEnergy within an object

Energy in the universe is constant, though it changes forms.

Law of Conservation of energyLaw of Conservation of energy – energy can neither be created nor destroyed

Forms of Energy Mechanical Chemical Electrical Nuclear Radiant

Mechanical Energy The total kinetic and potential energy of a

system Examples- lifting weights, chewing food,

opening the refrigerator

Chemical Energy The energy resulting from the forming or

breaking of bonds in a chemical reaction Endothermic reaction- A reaction whose

products have less total heat than the reactants

Exothermic reaction- where energy is released during the reaction

Electrical Energy Energy that is produced by the movement of

electrons Example- electricity

Radiant Energy Energy transmitted in the form of waves through

space or some medium. Also known as the electromagnetic spectrum Examples- light, radio waves, UV waves,

microwaves A microwave oven has a magnetron, which is an

electron tube that converts electrical energy into microwaves

The more water in food, the faster a microwave oven will cook it since the energy agitates water molecules

Nuclear Energy Energy from the splitting or combining of

atoms of certain elements that then gives off radiation

Examples- X-rays, nuclear power plants, irradiation

Heat vs. TemperatureTemperature and heat are not the same thing.

Temperature- the measure of the average kinetic energy of a group of individual molecules

Heat- describes amount of energy transferred from one object to another caused by a temperature difference between the two bodies

Describing Energy ChangesHeat flow is from the warmer object to

the cooler object

Heat Flow

Heat Flow

Describing Energy ChangesHot day 50°C = 122°F

Beans lost energy, it was transferred to its surroundings. This change of energy would be negative change = ∆

Energy transferred from fire to beans. Change in energy for beans would be positive.

Endothermic reactions – absorbs heat, ∆H is positive, the surroundings cool down

Exothermic reactions – releases heat, ∆H is negative, the surroundings heat up

Heat

Surroundings

Heat

Surroundings

Describing Energy Changes

Feels cold to the touch

Feels warm to the touch

Heat Transfer Three methods of heat transfer Conduction- the transfer of heat through

matter from particle to particle collisions Convection- the transfer of heat by the

motion of fluids, such as water and air Radiation- the transfer of heat by

electromagnetic waves

Units used to describe Energy:

calorie – called “little calorie” – (cal)

kilocalorie – called “Big calorie”- (CAL) 1000 calories – same as a food calorie

Joule – the SI unit of heat - (J)

CONVERSION FACTOR

1 cal = 4.184 joules

1 cal 4.184 J

4.184 J 1 cal

Energy Flow and Phase Changes Fusion- The movement from a solid to a

liquid phase, aka melting Crystallization- The movement from a liquid

to a solid phase, aka freezing Latent heat of Fusion- The energy needed to

melt or freeze a substance

Energy Flow and Phase Changes Evaporation or Vaporization- The phase

change from the liquid to the gaseous phase Condensation or Liquefaction- The change of

a gas to a liquid Latent heat of vaporization- The amount of

heat needed to either evaporate or condense a substance

Energy Flow and Phase Changes Latent heat- The energy required to complete

a phase change without a change in temperature

Deposition- The changing of a substance directly from a gas to a solid, ex. Frost forming on a window

Sublimation- The changing of a substance directly from a solid to a gas

Phase Change Diagram