We ll cut through this one. :) CHOPPED-UP CHAPTER

Transcription

1 We ll cut through this one. :) CHOPPED-UP CHAPTER

2 ENERGY CHAPTER 10

3 WHAT DO YOU KNOW? What first comes to your mind when you hear the term energy? What do calories measure? List three sources of energy. Have you heard of the term entropy? What does it mean?

4 HERE WE WILL... understand the general properties of energy understand the concepts of temperature and heat understand the direction of energy flow as heat

5 10.1 THE NATURE OF ENERGY Energy is the ability to do work or produce heat

6 can be classified as kinetic or potential kinetic = energy due to motion potential = energy due to position

7 one of the fundamental characteristics of energy is that it is conserved it is changed in form but not created or destroyed in a typical rxn this the law of conservation of energy

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13 10.2 TEMPERATURE AND HEAT the temp of something is a reflection of the vigor of the random motions of the components of that substance

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17 heat is a flow of E between two objects due to a temp difference in the two objects notice here that matter has a boundary; energy does not

18 on the next slide, notice that there was a heat flow b/t the two sides that were different T s which way did it flow?...

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21 the random motions of the components of an object constitute the thermal energy of that object the flow of energy called heat is the way in which thermal energy is transferred from a hot object to a colder object

22 10.3 EXO- AND ENDOTHERMIC what is this????

23 in an exothermic rxn, E flows from system surroundings in an endothermic rxn, E flows from surroundings system exo often feel warmer (like fire); endo often feel cooler

24 FRINKING FRAP TIME Exo or Endo process? (from point of view of bold things) 1. Your hand gets cold when you touch ice. 2. The ice melts when you touch it. (think!) 3. Ice cream melts. 4. Propane burns in a propane torch. 5. After swimming, water drops on your skin evaporate. 6. Two chemicals mixing in a beaker give off heat.

25 WALK AWAY WITH...1A energy is conserved the law of conservation of energy says that energy is neither created nor destroyed in a chemical process energy can be changed from one form to another but the total amt of E remains the same

26 WALK AWAY WITH...1B energy is classified as either kinetic or potential kinetic due to motion, potential due to position

27 WALK AWAY WITH...2 temperature indicates the vigor of the random motions of the components of that substance heat is the flow of energy b/t two objects b/c of a temp diff exothermic is where heat flows from system to surroundings endothermic is opposite

28 HERE WE WILL... understand how heat is measured understand energy as a driving force for natural processes understand the basic concept of entropy

29 10.4 THERMODYNAMICS thermodynamics is the study of E and its changes from Gk therme ϑέρµη (heat) + dynamikós δυναµικός (force or power) internal E of a system is the sum of the kinetic (due to motion) and the potential (due to position) E s of a substance

30 10.5 MEASURING ENERGY CHANGES a calorimeter [L. calor = heat] is used to measure the heat of chemical reactions units used are joules (but also calories)

31 (low joule products)

32 to measure E changes you need to know 1) the T change ( C) of your sample... (which takes more energy: to heat this pool by 10 C or by 20 C?)

33 and 2) the amount of substance being heated (g)... (Which takes more energy? to heat this cup of water 10 C or the pool?)

34 and 3) the specific heat capacity of a substance i.e. E required to change the temp of 1 gram by 1 degree C water has an enormous heat capacity (4.18 J/g C), sand not so much (0.8 J/g C)...

35 that s why wet sand is so much cooler and easier to walk through on a hot day than dry sand - same amount of sunlight, but the water absorbs a lot of heat as its temp rises slooooowly

36 which is why we can do this

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39 all three (mass, change in T, sp/heat/cap) can be used to calculate the changes in energy that occur in reactions or special circumstances ready?

40 Q = sm T Q = heat (J) s = specific heat capacity (a constant, measured in J/g C) m = mass (g) T = change in T ( C)

41 EXAMPLE 1.6 g of a mystery gold-like metal requires 5.8 J of energy to change its T from 23 C to 41 C. Is it gold? (s Au = 0.13 J/g C) solve for s, so: s = Q/m T s = 5.8/(1.6 x 18) s = 0.20 J/g C, so not gold!

42 QUICK QUIZ You want to heat a mug of tea (250 g) from room temp, 25 C to 100 C. How much E would you need? (sh2o for water = J/g C) Q = sm T Q = (4.184)(250)(75) Q = 78,000 J Q = 78 kj

43 10.10 ENERGY AS A DRIVING FORCE Why does a log burn to ash, but ash never gathers to make a log? Why does a toot spread throughout a room, but not gather in one place again? two important things we ve figured out in science: nature likes to spread energy around nature likes to spread matter around

44 If both energy spreading and matter spreading take place, your reaction will go. (like an explosion) If neither, then it won t happen by itself. (like CO2 and H2O getting together to make sugar) If both are competing, like hydrogen and oxygen getting together (bad) but giving off energy when it does (good!) it depends on other things like temperature. (too complicated to figure out now) but what is this matter spreading out business?...

45 ENTROPY entropy (S) is a way of keeping track of the randomness of a process the lower the entropy the more ordered it is (like ice or a Lego creation) the higher the entropy the more disordered (like steam or your room)

46 since the tendency is for E and matter to spread, the entropy of the universe is increasing. = second law of thermodynamics thus the universe is headed toward total randomness. Woo oho! :)

47 WALK AWAY WITH...1 thermodynamics is the study of energy and its changes the common units for heat are calories and joules the amount of heat (Q) involved can be found Q = sm T

48 WALK AWAY WITH...2 natural processes occur in the direction that leads to an increase in the disorder (increase in entropy) of the universe the principal driving forces for natural forces can be described in terms of matter spread or energy spread

49 10EOCS 14, 24, 26, 52

50 quiz time...

51 Chapter 10 Chop Quiz 1. Energy of position, that is, energy which depends on where something is, is also called... A. kinetic energy B. potential energy C. heat energy D. enthalpy

52 Chapter 10 Chop Quiz 2. Temperature is A. a measure of the potential energy stored in a substance. B. the same as heat. C. a measure of the random motion of the particles of a system.

53 Chapter 10 Chop Quiz 3. Which of the following processes is exothermic? A. candle wax melting B. a puddle evaporating C. dry ice subliming (evaporating) to form gaseous carbon dioxide D. propane burning in a propane torch

54 Chapter 10 Chop Quiz 4. Water has a relatively specific heat capacity, meaning it responds rather to cooling or heating. A. low, quickly B. low, slowly C. high, slowly D. high, quickly

55 Chapter 10 Chop Quiz 5. What two events drive nature? A. matter spreading, energy spreading B. matter coming together, energy spreading C. matter spreading, energy coming together D. matter coming together, energy coming together

56 Chapter 10 Chop Quiz 6. What is the study of energy and its changes? A. calorimetry B. thermodynamics C. the law of conservation of energy D. calorodynamicsmittywerbermannjensen

57 Chapter 10 Chop Quiz 2 points each... Q = sm T 7. Calculate the heat given off when 45.0 g of water cools from 45 C to 22 C. The specific heat of water is J/g C 8. A sample of water requires 200 J to be heated 1.7 C. What mass of water is present? Turn in when you are finished!

58 answers...

59 Chapter 10 Chop Quiz 1. Energy of position, that is, energy which depends on where something is, is also called... A. kinetic energy B. potential energy C. heat energy D. enthalpy

60 Chapter 10 Chop Quiz 2. Temperature is A. a measure of the potential energy stored in a substance. B. the same as heat. C. a measure of the random motion of the particles of a system.

61 Chapter 10 Chop Quiz 3. Which of the following processes is exothermic? A. candle wax melting B. a puddle evaporating C. dry ice subliming (evaporating) to form gaseous carbon dioxide D. propane burning in a propane torch

62 Chapter 10 Chop Quiz 4. Water has a relatively specific heat capacity, meaning it responds rather to cooling or heating. A. low, quickly B. low, slowly C. high, slowly D. high, quickly

63 Chapter 10 Chop Quiz 5. What two events drive nature? A. matter spreading, energy spreading B. matter coming together, energy spreading C. matter spreading, energy coming together D. matter coming together, energy coming together

64 Chapter 10 Chop Quiz 6. What is the study of energy and its changes? A. calorimetry B. thermodynamics C. the law of conservation of energy D. calorodynamicsmittywerbermannjensen

65 Chapter 10 Chop Quiz 2 points each... Q = sm T 7. Calculate the heat given off when 45.0 g of water cools from 45 C to 22 C. The specific heat of water is J/g C 4300 J 8. A sample of water requires 200 J to be heated 1.7 C. What mass of water is present? 28 g

66 EOC ANSWERS