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Chapter 3

Chapter 3. Scientific Measurements. Describe the following object in your notes. Qualitative vs. Quantitative. Qualitative: gives results in a descriptive nonnumeric form Ex: large & small Quantitative: gives results in a definite form, usually in numbers Ex: 121cm. Good accuracy.

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Chapter 3

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  1. Chapter 3 Scientific Measurements

  2. Describe the following object in your notes

  3. Qualitative vs. Quantitative Qualitative: gives results in a descriptive nonnumeric form Ex: large & small Quantitative: gives results in a definite form, usually in numbers Ex: 121cm

  4. Good accuracy Accuracy vs. Precision Accuracy: is a measure of how close a measurement comes to the actual or true value. Correctness Poor accuracy results from procedural or equipment flaws

  5. Good precision Accuracy vs Precision Precision: is a measure of how close a series of measurements are to one another. Reproducibility Poor precision results from poor technique

  6. Determining Error

  7. What is the percent error of a measured value of 114 lbs if the person’s actual weight is 107 lbs?

  8. Scientific Notation • Used when working with large or very small numbers • #’s less than 1 have negative exponents • 0.00036 = 3.6 x 10-4 • #’s greater than 1 have positive exponents • 36,000 = 3.6 x 104

  9. DO NOW: Significant Figures

  10. DO NOW: Significant Figures The following measurements are not in the correct sig. figs. Rewrite them so that they show the correct number of sig. figs. Put all answers in scientific notation. Wrong measurements correct Correct Answers sig. figs. 1. 314.721 m 4 3.147 x 102 2. 0.00177 cm 2 1.8 x 10-3 3. 64.32 x 10-1 dm 1 6 4. 8792 L 2 8.8 x 103 5. 591,000,000 L 4 5.910 x 108

  11. Dimensional analysis • The skill of converting from one unit to another EX: 10 meters is how many millimeters 13 days is how many seconds

  12. Units Get Larger (always make larger unit = 1) Katie Hates Dogs b/c Dogs Can’t Meow

  13. Conversion Factor • A fraction that always equals 1. EX: 1km = 1,000m put into a fraction 1 km or 1,000m 1,000m 1 km Both fractions equal 1

  14. EXAMPLE Problem #1: 12 m=?cm STEPS 1. Write the given 12m 2. Draw the conversion line 12m 3. Find a conversion factor. 100cm = 1m 4. Place what unit you want to get rid of opposite the given. 12mm

  15. 5. Place the unit you want at the same level as the given. 12m cm m 6. Fill in the #’s of the conversion factor. 12m 100 cm 1m 7. Cancel units 12m 100 cm 1m 8. Multiply everything on top, multiply everything on the bottom, and then divide SO……….12m = 1,200cm

  16. Chapter 17 Thermochemistry

  17. Thermochemistry The study of energy changes that occur during chemical reactions and changes in state.

  18. Thermochemistry Energy: the ability to do work or to supply heat ENERGY (Joule or calorie) = HEAT (J or cal) 1 cal = 4.18 J Chemical Potential Energy: stored energy in chemicals

  19. Heat vs. Temp. Heat and temperature are concepts that are often confused

  20. Calorie vs. calorie Calorie = refers to food (dietary) Calorie = 1kilocalorie = 1,000 calories Snickers Bar = 280 Calories = 280 kilocalories = 280,000 calories calorie= a unit of heat

  21. Specific Heat Capacity The amount of heat it takes to raise the temperature of 1 g of a substance 1oC q =m ΔT Cp q =heat energy (J or cal) m =mass (g) ΔT =(Tf – Ti) = oC Cp = specific heat = J = heat (J) g x oC mass (g) x (Tf – Ti)

  22. Q =m Δ T Cp q = g oC J g x oC When units are canceled, q = Joules

  23. Specific Heat Capacity The amount of heat it takes to raise the temperature of 1 g of a substance 1oC For example: WATER VS. METAL -Higher the specific heat: the less fluctuation of heat and therefore the less fluctuation of the temp. of the object.

  24. Exothermic vs. Endothermic Exothermic: a process in which heat is released to the surrounding • The system loses heat as the surroundings heat up • q has a negative value because the system is losing heat Endothermic: a process in which the system gains heat as the surroundings cool down • Heat flows into a system • q has a positive value because the system is gaining heat

  25. Calorimetry To measure specific heat capacity a bomb calorimeter is used. Calorimetry is based on the principle: Law of conservation of energy

  26. Bomb Calorimeter

  27. Plastic Cup Calorimeter

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