1. Thermodynamics the study of energy changes in reactions

2. Energy Energy is the ability to do work or produce heat. Energy is divided into two basic types: potential energy kinetic energy.

3. Potential Energy Potential energy is stored energy based on: position - gravity-related, like a skateboarder at the top of a half-pipe or stretched rubber band chemical composition - like the chemicals in food or a battery

4. Kinetic energy Kinetic energy is energy of motion This includes the constant, random motion of atoms and molecules Is proportional to temperature As temp increases, motion of particles increases →Thermal Expansion

6. Chemical Energy – Form of potential energy based upon chemical composition – Stored in bonds between atoms, molecules, and ionic crystals – Potential to form new substance Do work produce or require heat – Chemical energy of food powers your body – Chemical energy of gas powers your car

7. Thermal Energy: Total internal energy of system: depends on both Heat and Temperature Heat: Form of energy that flows from warmer to cooler object Temperature: measure of the average KE of the particles

8. Energy can be converted between the different forms of energy, but no matter how many times energy is converted the Law of Conservation of Energy States no energy can be created or destroyed

9. Heat (q): energy that moves from hot to cold Will continue to flow until temps are equal Heat is quantified by measuring change in temp, Temp does not directly measure heat 20°C10°C stored What is final temp?

10. calorie: To measure heat directly, the calorie (cal) was defined as the amount of heat needed to increase the temp of 1 gram of water by 1 °C.

11. Note: The Calories reported on food wrappers are measured as heat needed to increase the temperature of 1000 grams of water by 1 °C, 1 Calorie (Cal) = 1000 calories (cal) = 1 kilocalorie (kcal) Drinking a whole can of Pepsi actually means drinking: 250 Cal = 250,000 calories! Normal diet: 2,000 Cal = 2,000,000 cal

12. Calorimetry: measuring heat energy Calorimeter: device used to measure heat lost or absorbed during chemical reaction, including energy from food

13. Joule: measure energy more accurately Calories are still used in the nutrition field, but in chemistry we use the Joule (J). 1 cal = 4.184 J If my breakfast contains 230 Calories, how much energy in Joules will it supply?

14. Joule: measure energy more accurately Calories are still used in the nutrition field, but in chemistry we use the Joule (J). 1 cal = 4.184 J If my breakfast contains 230 Calories, how much energy in Joules will it supply? 230 Cal 1000 cal 4.184 J 1 Cal 1 cal

15. Joule: measure energy more accurately Calories are still used in the nutrition field, but in chemistry we use the Joule (J). 1 cal = 4.18 J If my breakfast contains 230 Calories, how much energy in Joules will it supply? 230 Cal 1000 cal 4.18 J = 961400 J 1 Cal 1 cal = 9.6 x 10 5 J

16. Both the calorie and Joule are defined using water But, other substances gain and lose heat at different rates Specific heat (c) – the amount of energy required to raise 1 gram of a any substance by 1°C Liquid water has a relatively high specific heat: loses & gains heat slowly – moderates earth’s climate

18. The better the conductor, the lower the specific heat

19. When a cake has been baked & removed from the oven it would cause severe burns to touch the metal pan, but the top of the cake can be touched to test if the cake is ready…Why?

20. The metal of the pan has a low specific heat b/c it can lose heat quickly This heat would be absorbed by your finger!!! The cake contains a lot of trapped air and other materials with much higher specific heats. These objects lose heat slowly, allowing more time before your finger has absorbed enough heat to cause a burn.

21. Density of a cake is much less than the density of the metal pan, so for the same surface area touched by your finger there are a lot more metal atoms that transfer heat energy than cake molecules. So… the mass also has an affect on the amount of heat transferred

22. Plus… (old stuff) Metals are good conductors of heat and electricity While air is a poor conductor of heat and electricity (nonmetals)

23. To calculate the amount of heat gained or lost by an object q = m × c × ∆T q = heat (J) m = mass (g) c = specific heat ∆T = Temp. final – Temp. initial, in °C J g °C

24. If the object is heating up: the final temp is greater than the initial temp, so ∆T is positive and amount of heat gained is positive. + q

25. If the object is cooling down: the final temp is less than the initial temp, so ∆T is negative and the amount of heat lost is negative. - q

26. If ∆T is positive the answer for heat is positive: heat is gained. If ∆T is negative the answer for heat is negative: heat is lost. - q+ q

27. Ex. 1) What is the heat absorbed by 100 g of water to raise it from 25 °C to 75 °C? The specific heat of water is 4.184 J/g°C. q = m × c × ∆T q = ________ x ________ x (________ - _______) q = _______________

28. Ex. 1) What is the heat absorbed by 100. g of water to raise it from 25 °C to 75 °C? The specific heat of water is 4.184 J/g°C. q = m × c × ∆T q = _100__ x _4.184_ x (__75_ - _25__) q = __ 20920 J___ = 2.1 x 10 4 J

29. Ex. 2) What is the heat given off by 100 g of iron to cool from 50 °C to 20 °C? The specific heat of iron is 0.449 J/g°C. q = m × c × ∆T q = ________ x ________ x (________ - _______) q = _______________

30. Ex. 2) What is the heat given off by 100 g of iron to cool from 50 °C to 20 °C? The specific heat of iron is 0.449 J/g°C. q = m × c × ∆T q = 100 x 0.449 x ( 20 - 50) q = 100 x 0.449 x (-30) q = -1347 J = -1 x 10 3 J

31. Heat Movement The Law of Conservation of Energy states that heat energy cannot just appear out of nowhere and disappear to nowhere. If an object warms up, that heat had to be absorbed from somewhere and if an object cools down, that heat had to be given off to something.

32. In the Earth’s ecosystem heat is gained by the sun’s radiation and given off to space at night. This is why a cloudy night is typically warmer than a clear night – the heat gets trapped in by the clouds.

34. Heat can move from one object to another by three ways: 1.Radiation 2.Convection 3.Conduction

36. The energy from the sun reaches earth by radiation - electromagnetic waves: The infrared part of the electromagnetic spectrum is the “heat” form of radiation. How hot can it get? Ex: heat from fire, light bulb, coil on electric stove

37. Convection is the movement of heat by circulating materials, so anything that is a fluid (gases and liquids) can move heat by convection, often called convection currents. Ex. Most air-conditioning systems, the ocean currents, and the warm and cold “fronts” the weather-person talks about on the news.

39. Conduction is the movement of heat between objects that are touching. Most common form of heat movement when cooking. The food touches a pan that’s touching a burner. As the pan absorbs heat from burner the food absorbs heat from the pan.

40. When you touch a hot pan heat moves from the pan into your hand which then burns you. Often the lasting effects of a burn can be minimized if you can quickly get the heat to move out of your hand by running cold water over your hand for a long time.

41. Heat energy will always naturally move from an object with higher heat to an object with lower heat, regardless of the method of heat transfer

42. The Law of Conservation of Energy also tells us that the amount of heat lost by the hot object must be equal to the amount of heat gained by the cold object. 20°C10°C 15°C

43. Hot becomes cooler, and cold becomes warmer. -q lost = q gained -- (m lost × c lost × ∆T lost ) = m gained × c gained × ∆T gained

44. Phases or States of Matter: Solid, Liquid, Gas Sometimes when an object gains or loses heat, it is not just the temperature that changes but the phase of the object can change. The phase depends on how much heat energy is in the object, often measured by the temperature. The solid will have lower temperature than the liquid form, which will have lower temperature than the gas (vapor) form.

45. Energy in states of matter H i energy & velocity - Low attractive forces & density Hi temp Gas Energy Liquid Energy Released In Solid Low energy & velocity - Hi attractive forces & density Low temp EndothermicExothermic

46. +q: heat is added or absorbed – Endothermic –q: heat is lost or released – Exothermic Phase changes occur when sufficient heat energy is added or removed

47. From this heat curve (for water) we can see how the temperatures change and the phases change. Notice that the temperature does not change during a phase change (the two flat lines).

48. Heat & Chemical Reactions Thermochemical Equations: A balanced chemical equation that includes all physical states (s, l, g) and change in enthalpy (H) (heat content). 4 Fe(s) + 3O 2 (g) → 2Fe 2 O 3 (s) + 1625 kJ Heat can be written as either a reactant or product Every chemical reaction involves a change in energy: heat and/or light. Heat released

49. If a chemical reaction feels cold: absorbing heat. endothermic reaction – energy in heat energy is written on the reactant side q is positive (+q) 27 kJ + NH 4 NO 3 (s) → NH 4 + (aq) + NO 3 - (aq) Heat Added

50. If a chemical reaction feels warm, giving off heat. exothermic reaction - energy out heat energy is written on the product side q is negative (-q) 4 Fe(s) + 3O 2 (g) → 2Fe 2 O 3 (s) + 1625 kJ Heat released

51. Endothermic (a reactant) solid + energy (heat) → liquid Heat flows into the system from the surroundings. This is why your skin gets cold when you hold ice; the heat is flowing out of your skin to melt the ice. System: ice Surrounding: your skin

52. Exothermic (a product) Iron + oxygen → iron(III) oxide + energy (heat) heat is released from the system and is absorbed by the surrounding environment which is why it’s used in instant hot pads. System: hot pad Surrounding: your skin

53. Enthalpy (H): total heat energy of system ∆H = change in enthalpy Exothermic Endothermic ∆H is negative ∆H is positive Energy of system decreased increased decreased

54. To separate water into hydrogen and oxygen (electrolysis) electricity is often used. 2H 2 O  2H 2 + O 2 Is electrolysis of water endothermic or exothermic? Where does the energy “go” in the equation?

55. The enthalpy of reaction (∆H) can be calculated to determine if heat is released or gained. (STAAR Chart) ΔH = ∆H f o (products) - ∆H f o (reactants) ∆H f o = standard enthalpy (heat) of formation from the formation of 1 mole of compound - add up from given values

56. If ΔH is +, then heat is absorbed, so it is an endothermic reaction If ΔH is -, then heat is released, so it is an exothermic reaction

57. Ex. Find the ∆H rxn for liquid ethanol, C 2 H 5 OH, undergoing combustion: C 2 H 5 OH + 3O 2 → 2CO 2 + 3H 2 O Is this an endothermic or exothermic reaction? Thermodynamic values table Compound ∆H f o C 2 H 5 OH-277.69 kJ/mol O 2 0 kJ/mol CO 2 -393.509 kJ/mol H 2 O-285.830 kJ/mol

58. Ex. Find the ∆H rxn for liquid ethanol, C 2 H 5 OH, undergoing combustion: C 2 H 5 OH + 3O 2 → 2CO 2 + 3H 2 O Is this an endothermic or exothermic reaction? Thermodynamic values table Compound ∆H f o C 2 H 5 OH-277.69 kJ/mol O 2 0 kJ/mol CO 2 -393.509 kJ/mol H 2 O-285.830 kJ/mol ∆H f o (reactants): ∆H f o (products): ΔH = ∆H f o (products) - ∆H f o (reactants)

59. Ex. Find the ∆H rxn for liquid ethanol, C 2 H 5 OH, undergoing combustion: C 2 H 5 OH + 3O 2 → 2CO 2 + 3H 2 O Is this an endothermic or exothermic reaction? Thermodynamic values table Compound ∆H f o C 2 H 5 OH-277.69 kJ/mol O 2 0 kJ/mol CO 2 -393.509 kJ/mol H 2 O-285.830 kJ/mol ∆H f o (reactants): (-277.69) + 3(0) = -277.69 kJ ∆H f o (products): 2(-393.509) +3(-285.830) = -787.018 + (-857.49) = -1644.508 kJ ΔH = ∆H f o (products) - ∆H f o (reactants) = (-1644.508) – (-277.69) = -1366.818 kJ Per mole

60. Ex. Find the ∆H rxn for liquid ethanol, C 2 H 5 OH, undergoing combustion: C 2 H 5 OH + 3O 2 → 2CO 2 + 3H 2 O Is this an endothermic or exothermic reaction? Thermodynamic values table Compound ∆H f o C 2 H 5 OH-277.69 kJ/mol O 2 0 kJ/mol CO 2 -393.509 kJ/mol H 2 O-285.830 kJ/mol ∆H f o (reactants): (-277.69) + 3(0) = -277.69 kJ ∆H f o (products): 2(-393.509) +3(-285.830) = -787.018 + (-857.49) = -1644.508 kJ ΔH = ∆H f o (products) - ∆H f o (reactants) = (-1644.508) – (-277.69) = -1366.818 kJ Neg = Exothermic Per mole

61. An additional way to show a change in enthalpy without a calculation is with an enthalpy diagram. What is the key to knowing if the diagram shows exothermic or endothermic? Energy in or out