Chapter 2

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Chapter 2

  1. 1. Chapter 2 Energy
  2. 2. ‘‘If I have seen further, it is because I have stood on the shoulders of giants. ” Sir Isaac Newton :
  3. 3. Energy and Change 0 Energy — Capacity to do work - If there is a change in matter either physical or chemical, energy is involved 0 System — Substances in consideration 0 Surroundings — Rest of the Universe
  4. 4. Energy and Change 0 Exothermic — Energy is released from the system in the form of heat (feels hot) 0 Endothermic — energy is absorbed from the system in the form of heat (feels cold)
  5. 5. Energy and Change 0 Law of Conservation of Energy — Energy cannot be created or destroyed, but can only change from one form to another. — Heat -> Chemical
  6. 6. I. Energy - Surroundings System Before reaction Surroundings System After reaction
  7. 7. is Heat — Energy transferred from objects of higher temperatures to objects of lower temperature. ii Kinetic Energy — Energy of motion
  8. 8. is 4'! " ‘- '~ I in. A s Temperature is a relative measure of the average kinetic energy of he molecules. ii There are 4 major scales of temperature. - You are most familiar with the Fahrenheit scale, but we will use the Celsius and Kelvin scales.
  9. 9. t(°C) = T(K) - 273K T(K) = t (°c) + 273K
  10. 10. Fahrenheit Celsius Kelvin water bofls . ... ... ... ... ... ... ... ..212° . ... ... ... .. . .1oo° . ... ... ... .. . . 373 . ... ... .. . . 1 Body tempefatufe . . . . . . . . . . . ..98_6° . . . . . . . . . . . . . . 37° . . . . . . . . . . . . . . . . . . . . . . . .. Roof“ tefnpefatufe . . . . . . . . . . . .. 63° . . . . . . . . . . . . . H200 . . . . . . . . . . . . . . . . . . . . . . . .. Water freezes . ... ... ... ... ... ... . . .32° . ... ... ... ... . . . 0° . ... ... ... .. . . 273 . ... ... .. . . k 4 3
  11. 11. it A transfer of heat may not affect the temperature of a system. ii This is because the energy going in a heat is being used to break bonds it Heat transfer affect substances differently. The amount of energy required to raise the temperature is called Specific Heat.
  12. 12. Temperature Melting point Heat of vaporization . Energy added as heat
  13. 13. Chapter 2 Study of Matter and Energy :
  14. 14. “The best way to have good ideas is to have lots of ideas” Linus Pauling :
  15. 15. The Scientific Method 0 Scientific Method is a series of steps followed to solve a problem. (See page 46 in text book) 0 This is NOT a formula, but a general method. .. meaning it may be altered.
  16. 16. The Scientific Method 0 The Jonesian Method 2 Data - Observations (You do this everyday) 3 Law — Generalized data, NOT explanation 4. Hypothesis — Guess based on law 5 Experiment — Controlled Test 6 Theory — Explanation of law
  17. 17. The Scientific Method Wood burns, shrinks, and turns black 2. All wood, when burned, will shrink and turn black 3. Upon combustion “ph| ogiston” leaves the wood 4. Mass of wood (25 g) Vs. Mass of smoke + ash (27 g) 5. “Ph| ogiston” does not leave wood, in fact wood combines with something. (Oxygen from the air)
  18. 18. “You must collect things for reasons you don’t yet understand. ” Daniel J. Boorstin :
  19. 19. The Scientific Method 1. My car won’t start 2. The engine is not turning over 3. The battery is dead 4. Replace battery, start car 5. The battery was dead
  20. 20. “Scientific thought is not accompaniment of human progress, but human progress itself. ” William Kingdon Clifford
  21. 21. The Scientific Method 0 Modeling is a way to help understand the microscopic world of chemistry 0 Models represents an object, system, process, or idea
  22. 22. Chapter 2 Measurement and Calculations in Chemistry
  23. 23. Accuracy and Precision 0 Application of mathematics! 0 Exact numbers - counting, some conversions 0 Measured numbers — equipment and humans make errors, therefore these number are NOT exact, they have uncertainties
  24. 24. Accuracy and Precision 0 Uncertainty - The last digit in a measured number is estimated. — Example: 0.81cm (0.80 — 0.82)
  25. 25. Accuracy and Precision O 0 ' . h 0 ‘ H . .’ ‘ High Accuracy Low Accuracy Low Precision High Precision
  26. 26. Significant Figures (Sig Figs) 0 Sig Figs are determined by the precision of the measurement 0 See the rules on page 57
  27. 27. Significant Figures 0 Adding and Subtracting - # of decimal places = least number of decimal places — Eg 11.93g+3.2g= 15.1 g
  28. 28. Significant Figures 0 Multiplying and Dividing - # of sig figs = least number of sig figs 0 3.31 X 2.2 in = 7.3 in?

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