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Energy & Chemical Change

Energy & Chemical Change. Chapter 16. 16.1 Energy. Discovery Lab page 489. A. The Nature of Energy. Energy: ability to do work Potential Energy: energy due to composition or position of an object Kinetic Energy: energy of motion.

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Energy & Chemical Change

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  1. Energy & Chemical Change Chapter 16

  2. 16.1 Energy • Discovery Lab page 489

  3. A. The Nature of Energy • Energy: ability to do work • Potential Energy: energy due to composition or position of an object • Kinetic Energy: energy of motion

  4. Kinetic energy of a substance is directly related to the constant random motion of it particles and is proportional to temperature.

  5. Potential energy of a substance depends upon its composition • Type of atoms • # & type of chemical bonds • How atoms are arranged

  6. 1. Law of conservation of energy • States that in any chemical reaction or physical process, energy can be converted from one form to another, but it is neither created nor destroyed

  7. 2. Chemical potential energy • Energy stored in a substance because of its composition • Gasoline • Many times much of the potential is released as heat • Heat (q): process of flowing from a warmer object to a cooler object

  8. 3. Measuring Heat • Calorie: amount of heat required to raise temperature of one gram of pure water one degree Celsius • Joule: SI unit of heat & energy • 1 joule = .2390 calories • 1 calorie = 4.184 joules • Practice Problems p.492

  9. B. Specific Heat • Amount of heat required to raise the temperature of one gram of that substance by one degree Celsius

  10. Calculating heat evolved & absorbed q = c x m x T q = heat absorbed or released c = specific heat of substance m = mass of sample in grams T = difference between final temperature & initial temperature

  11. 16.2 Heat in Chemical Reactions & Processes

  12. A. Measuring Heat • Calorimeter is an insulated device used for measuring the amount of heat absorbed or released during a chemical or physical process

  13. B. Chemical Energy & Universe • System: specific part of universe that contains reaction or process • Surroundings: everything in the universe other than the system • Universe = system + surroundings

  14. 1. Enthalpy & Entropy changes • Enthalpy: (H) heat content of a system at constant pressure • Can’t measure actual energy or enthalpy of a substance, you can measure change in enthalpy, which is heat absorbed or released in a chemical reaction

  15. Enthalpy (heat) of reaction: (Hrxn) change in enthalpy for a reaction • (Hrxn) = Hfinal – Hinitial • (Hrxn) = Hproducts – Hreactants

  16. 2. Sign of enthalpy reaction • Exothermic Reactions: heat pack

  17. Endothermic Reactions: cold pack

  18. 16.3 Thermochemical Equations

  19. A. Writing Thermochemical Equations • Thermochemical Equation: is a balanced chemical equation that includes physical states of all reactants and products and the energy change • Negative H = exothermic • Positive H = endothermic

  20. B. Changes of State • Molar enthalpy (heat) of vaporization: (Hvap), heat required to vaporize one mole of a liquid • Molar enthalpy (heat) of fusion: (Hfus), heat required to melt one mole of a solid substance

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