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Chapter 2

Chapter 2. More chem – Less math. The Scientific Method. How do scientists do what they do? Can this method be applied to everyday life?. The scientific method is an approach to problem solving. It is a general strategy to provide a sound conclusion.

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Chapter 2

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  1. Chapter 2 More chem – Less math

  2. The Scientific Method How do scientists do what they do? Can this method be applied to everyday life?

  3. The scientific method is an approach to problem solving. It is a general strategy to provide a sound conclusion. At its most basic, the SM can be thought of as: Question → Possible answer → Test

  4. Hypothesis-possible hypothesis – possible answerans explanation Observation or question Experiment-testing hypothesis Conclusions Publishing – sharing results

  5. Conclusions from an experiment may lead to: Scientific Law – A description of something in nature. This may take the form of an equation. Examples: Scientific Theory – An explanation for something in nature supported by data. Examples: Model – A representation of something in nature. Examples:

  6. Experimental Control – Controls are used in experiments to give a basis of comparison or a baseline reading. Essentially, it answers the question, “What happens if I do nothing?” Examples:

  7. Serendipity Unexpected or unintended, but beneficial outcome of an experiment. Roentgen - Discovered X-Rays P. Spencer – Microwave use A. Fleming – Found penicillin Teflon – Searching for refrigerants

  8. Accuracy and Precision Descriptions of experimental data

  9. The Accuracy of experimental data indicates how well the data agree with known values. (How close to the bulls-eye). Ex: The actual mass of a beaker is 250.0 g. You measure the mass to be 249.2 g. Your accuracy would be good. Your partner measures the mass as 225.7 g – poor accuracy The Precision of experimental data indicates how consistent the data is. (How close the darts are to each other) Ex: You weigh the beaker 3 times and get 249.2, 259.4 and 238.8g. – Precision is poor. (But average accuracy is good) Your partner measures 225.7, 225.9, 226.0 g. –Precision is good – but accuracy is still poor.

  10. Energy Considerations In general, energy must be transferred or transformed during any chemical or physical change. The Law of Conservation of Energy says that energy cannot be created or destroyed in any chemical or physical change. In a chemical reaction, the total amount of energy must be the same on both sides of the equation.

  11. System – The reaction, process or object under study. Surroundings – The rest of the universe. Energy lost by one must be gained by the other and vice-versa!! Closed system – energy cannot leave or enter the system. Open system – energy is exchanged between system and surroundings. Examples:

  12. Kinetic energy – energy due to the motion of an object. Potential energy – energy due to the relative positions of objects!!!

  13. Forming chemical bonds releases energy Breaking bonds requires energy. Exothermic - Energy released to surroundings Endothermic - Energy absorbed from surroundings Chemical energy is the energy in matter due to chemical make-up. Can be thought of as stored in bonds.

  14. Heat and Temperature Heat can be described as the total amount of kinetic energy contained by a sample of matter. See Java Temperature is a measure of the average amount of KE of the particles of a sample of matter.

  15. 50oC 100oC What if they were filled with money rather than water? $50 bills $100 bills

  16. Specific Heat Capacity

  17. Temperature Scales Fahrenheit – 1724 – Commonly used in US. Based on freezing point of brine and “blood temperature” Celsius – 1742 – Anders Celsius. Developed by many scientists. Based on freezing and boiling point of pure water. Known as centigrade until 1948. Kelvin – Lord Kelvin (W. Thompson) 1848. Calculated as temperature where a gas has zero volume. Same size “degree” as Celsius.

  18. Conversions K = C + 273 (F+40)5/9 = (C+40) Or F=1.8 C +32 C= 0.56 (F-32)

  19. Practice: Average human body temperature is 98.6 oF. What is this temp in C and K? Lead (Pb) has a melting point of 327 oC. What is this temp in F and K? Nitrogen (N) boils at 77 K. What is this temp in C and F?

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