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Energy

Energy is defined as the ability to do work, with work being done when a force moves an object through a distance. It exists in various forms, primarily mechanical energy, which includes kinetic (motion) and potential (stored) energy. The unit of energy is the Joule (J), with 1 calorie equivalent to 4.19 Joules. Key principles include the conservation of energy, which states that energy cannot be created or destroyed, and the relationship between mass and energy as described by Einstein. Chemical reaction energy changes can be exothermic or endothermic, requiring activation energy to initiate.

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Energy

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  1. Energy

  2. Definition • Energy is the ability to do work • Work is done on an object whenever a force (push or pull) moves an object through a distance • Work = Force x Distance

  3. Forms of Energy • Mechanical energy –any energy possessed by macroscopic (visible) objects • Two kinds of mechanical energy Kinetic Energy Potential Energy

  4. Potential Energy • Stored energy that is available to do work at a later time

  5. Kinetic Energy • Energy of motion

  6. Unit of Energy • Joule (J) • Unit used to be the calorie (cal) • 1 cal = 4.19 J • How many joules is 1500 calories? • How many calories is 36 J?

  7. Conservation of Energy • Whatever changes occur in energy from one type to another, the total amount of energy remains constant • Energy cannot be created or destroyed

  8. Equivalence of Mass and Energy • Einstein found that matter and energy are related • Whenever there is a decrease in energy in a system, there is an increase in mass • Whenever mass increases, energy decreases

  9. New Conservation Law • Old conservation of matter and energy laws were combined • Law of Conservation of Mass and Energy – the total of mass and energy will remain constant in any reaction

  10. Energy in Reactions • In every change, there is a change in energy • Energy change usually more noticeable in chemical changes

  11. Exothermic • If reactants have more chemical energy than the products, then energy must be lost in reaction • This release in heat energy causes the substances to become hot • Chemical reactions that release heat are called EXOTHERMIC

  12. Endothermic Reactions • If products have more chemical energy than reactants, energy must be absorbed • The absorption of heat causes substances to feel cold • This is called an ENDOTHERMIC reaction

  13. Activation Energy • Even though some reactions are exothermic it may still require a little energy to start it off • This starting energy is called ACTIVATION ENERGY

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