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Food and Energy

Food and Energy. The Basics of Heat Transfer. The Flow of Energy. Thermochemistry - concerned with heat changes that occur during chemical reactions. Cranking up the Heat: Basic Thermodynamics. Energy - capacity of an object to do work or produce heat. Kinetic Energy.

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Food and Energy

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  1. Food and Energy The Basics of Heat Transfer

  2. The Flow of Energy Thermochemistry- concerned with heat changes that occur during chemical reactions

  3. Cranking up the Heat: Basic Thermodynamics Energy - capacity of an object to do work or produce heat

  4. Kinetic Energy • The energy an object has due to its motion Potential Energy • Stored energy • Energy of position

  5. External Energy The energy applied to an object by another source Internal Energy • Energy within an object

  6. Energy in the universe is constant, though it changes forms. Law of Conservation of energy – energy can neither be created nor destroyed

  7. Forms of Energy • Mechanical • Chemical • Electrical • Nuclear • Radiant

  8. Mechanical Energy • The total kinetic and potential energy of a system • Examples- lifting weights, chewing food, opening the refrigerator

  9. 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

  10. Electrical Energy • Energy that is produced by the movement of electrons • Example- electricity

  11. 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

  12. 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

  13. Heat vs. Temperature Temperature 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

  14. Describing Energy Changes Heat flow is from the warmer object to the cooler object Heat Flow Heat Flow

  15. Describing Energy Changes Hot day 50°C = 122°F Energy transferred from fire to beans. Change in energy for beans would be positive. Beans lost energy, it was transferred to its surroundings. This change of energy would be negative change = ∆

  16. Endothermic reactions – absorbs heat, ∆H is positive, the surroundings cool down Exothermic reactions – releases heat, ∆H is negative, the surroundings heat up Surroundings Heat Surroundings Describing Energy Changes Feels cold to the touch Feels warm to the touch Heat

  17. 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

  18. 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)

  19. CONVERSION FACTOR 1 cal = 4.184 joules 1 cal 4.184 J 4.184 J 1 cal

  20. 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

  21. 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

  22. 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

  23. Phase Change Diagram

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