Chapter 2. Secton 1 - Energy

Transcription

1 Chapter 2 Secton 1 - Energy

2 Energy and Change Energy is the capacity to do work Any change in matter involves energy Physical or chemical

3 Evaporation liquid gas Requires energy Hydrogen and oxygen react in an explosion to form water Energy is released (heat and light)

4 Endothermic processes absorb energy from the surroundings Melting/boiling of water (physical) Ice packs (chemical) (ammonium nitrate and water) Exothermic processes release energy Freezing/condensation of water (physical) Burning wood`

5 During a physical or chemical change, the total amount of energy does not change Law of Conservation of Energy System consists of components being studied at any given time Surroundings include everything outside the system HCl + H 2 O H 3 O + Cl - The HCl and H 2 O are the system, the beaker and air in/around are the surroundings

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7 Exothermic = Energy transfer from a system into the surrounding Endothermic = Energy transfer from surroundings into system Energy transfer comes in many forms Chemical, mechanical, light, heat, electrical, sound

8 Kinetic Energy Energy of motion Potential Energy Stored energy

9 Temperature - The measurement of the average kinetic energy of the molecules of a substance Heat is the energy transferred between objects at different temperatures (the sum of kinetic + potential energy) Hot Cold

10 So what s the difference??? Heat is energy. When heat (energy) goes into a substance one of two things happens: 1.) The temperature increases (this is what we think of) 2.) The substance can change state, without increasing the temperature

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12 Celsius Scale Zero point is freezing point of water Kelvin Scale Zero point is absolute zero The temp at which particles stop Converting! C = K K = C

13 Specific Heat Quantity of heat (energy) that must be transferred to raise the temp of 1 gram of substance 1 K. Metals Low specific heat Water High specific heat Unit for energy is Joule (J) Specific heat = J/g*K

14 Chapter 2 Section 2

15 The Scientific Method is a series of steps followed to solve problems 1.) Ask Question 2.) Research 3.) Hypothesis 4.) Test Hypothesis (Experiment) 5.) State Conclusion 6.) Report Results Things are often found by accident England Drug to treat malaria One experiment resulted in black sticky substance Mixed with alcohol created mauve (Synthetic purple dye)

16 Teflon 1938, DuPont chemist (Dr. Roy Plunkett) Trying to produce new coolant gas (refrigerant) Wanted to react tetrafluoroethene (TFE) with hydrochloric acid (HCl) Before he could do that, the TFE reacted with itself in a cylinder to form polytetrafluoroethene (chain molecules) This molecule proved to be very slippery!

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18 A proper experiment only has one variable Factors that affects results of an experiment A controlled experiment has only one variable Plant Experiment Miracle Grow, Pop, Salt Water, Gatorade Control?

19 Theory vs Law Scientific Law Statement or mathematical expression Describes an event or behavior Law of Conservation of Mass Scientific Theory Well tested explanations Can never be completely proven, but is not a guess

20 Models are simplistic representations of objects, systems, or processes

21 Chapter 2 Section 3

22 Accuracy vs Precision Accuracy is how close the measurement is to the actual value Precision is the exactness of a measurement (repeatability)

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24 Significant Figures are digits that are known with certainty, including one estimated, or uncertain digit Results must be recorded correctly! 1.) Nonzero digits are always significant 2.) Zeros between nonzero digits are significant 3.) Zeros in front of nonzero digits are not significant 4.) Zeros both at the end of a number and to the right of a decimal point are significant

25 Multiplication and Division Answers cannot have more sig figs than the measurement with the smallest number of sig figs Addition and Subtraction Result can be no more certain than the least certain number in the calculation If both, round after each operation

26 Some numbers have unlimited or no sig figs Count value Things that are counted (no sig figs) Conversion factors Unlimited sig figs

27 Scientific Notation Way of expressing large and small numbers Use to eliminate all place holding zeros Move decimal so only one number is to the left of decimal

28 Adding/Subtracting with Scientific Notation Most have same exponent before adding/subtracting Exponent then stays the same Multiplication First numbers are multiplied Exponents are added Division First numbers are divided Exponents are subtracted