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Energy & Chemical Change

Energy & Chemical Change. Energy – The ability to do work Potential Energy – due to composition or position Kinetic Energy – Due to motion Law of Conservation of Energy – In a chemical reaction energy can be converted from one form to another, but it is neither created or destroyed.

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Energy & Chemical Change

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  1. Energy & Chemical Change • Energy – The ability to do work • Potential Energy – due to composition or position • Kinetic Energy – Due to motion • Law of Conservation of Energy – In a chemical reaction energy can be converted from one form to another, but it is neither created or destroyed

  2. Chemical potential energy – the energy stored in a substance because of its composition • Heat – a measure of the amount of energy flowing from a warmer object to a cooler object

  3. Units of Heat • Calorie – the heat needed to raise the temperature of 1 gram of water 1oC • Calorie – nutritional calorie = 1,000 c • SI Unit = Joule 1c = 4.184 J • BTU – British Thermal Unit – the heat needed to raise 1 lb of water 1oF

  4. Specific Heat – c – amount of heat needed to raise the temperature of 1 g of a substance 1oC • For water – c = 1c/goC = 4.184J/goC

  5. Formula for the amount of heat transferred q = mc t • q = heat, m = mass, c = specific heat and t = change in temperature

  6. Calorimeter – an insulated device for measuring the amount of absorbed or released heat during a chemical or physical process • Exothermic reaction - heat is released • Endothermic reaction – heat is absorbed

  7. Enthalpy - H = change in energy • Hrxn = Hproducts - Hreactants • Exothermic = negative H • Endothermic = positive H

  8. Molar Enthalpy of Vaporization - Hvap - energy required to vaporize 1 mole of a substance at its boiling point • Molar Enthalpy of Fusion - Hfus – energy required to melt 1 mole of a substance at its melting point

  9. Hess’s Law – If 2 or more chemical equations can be added to produce a final equation, the sum of the enthalpy changes for the individual reactions is the enthalpy change for the final reaction.

  10. Standard Enthalpy of Formation - Hf – the change in enthalpy in the formation of one mole of the compound from its constituent elements • Each free element in its standard state has a Hf = 0

  11. Spontaneous process – a physical or chemical change that occurs without outside intervention • Entropy – S – a measure of the disorder or randomness • Law of Disorder – spontaneous processes always proceed in a direction to increase the disorder of the universe - S is positive

  12. Predicting Entropy Changes • Entropy increases when a solid changes to a liquid or a liquid changes to a gas • Entropy decreases when a gas dissolves in a liquid • Entropy increases when the number of gaseous product particles is greater than the number of gaseous reactant particles

  13. Usually the solvation of solids or liquids increases the entropy • Entropy is increased whenever the temperature of a substance is increased

  14. Gibbs free energy = G = H – T S • Reaction is spontaneous when G is negative

  15. Job Skills for the Future • Evaluate and Analyze • Think Critically • Solve Math Problems • Organize and Use References • Synthesize Ideas • Apply Ideas to New Areas • Be Creative • Make Decisions with Incomplete Information • Communicate in Many Modes Chemistry will develop ALL of these skills in YOU!

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