Thermochemistry branch of chem dealing with the relationship between chemical action and heat.

1. Thermochemistrybranch of chem dealing with the relationship between chemical action and heat. Applications of Heat and Energy

2. Energy • All energy can be classified as either potential or kinetic. • Potential energyis any type of energy that is stored. • Examples: batteries (stored chemical converts to electrical) • Top of a roller coaster hill (gravitational) • Candy Bar (stored energy in its chemical bonds) • Kinetic energy – any energy from the movement of matter.

3. Which has more heat - Lake Erie in December of a drop of boiling oil? • Frozen Lake Erie • Drop of boiling oil

4. Which has a higher temperature- Lake Erie in December of a drop of boiling oil? • Frozen Lake Erie • Drop of boiling oil

5. Heat vs. Temperature • Heat is the amount of energy that flows from a hotter object to a colder one. • It is the sum energy of all of the molecules in a substance • Temperature is the average kinetic energy of an object.

6. Heat Transfer • Heat always flows from an object with more heat (hotter) to an object with less heat. • Note: Something that is cold just lacks heat. There is no unit for “cold”. • When you feel cold, it is because you are losing heat (not gaining “cold”)

7. True or False: When you place ice cream in the freezer, heat is transferred from the ice cream to the freezer. • True • False

8. True or False: When we open the window, heat is transferred from your body to the air outside. • True • False

9. Units of Heat • Heat is measure in Joules (J). • (The joule is the SI unit for all types of energy.) • Example: when you heat a cup of tea, you use about 75,000J (or 75 kilojoules) of heat. Joule is pronounced jewel

10. Other units of heat • Heat is also measured in calories (cal). • 1000 calories equals a kilocalorie (Cal). • A calorie is the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius. • Also, 1 calorie = 4.184 Joules • And … 1 Cal = 4.184 kJ

11. What is the boiling point of water? • 100oF • 273K • 32oF • 212oC • 100oC

12. What is the freezing point of water? • 0oF • 32K • 100oF • 273K • 32oC

13. Units of Temperature

14. Units of Temperature TF = 1.8TC + 32 TK = TC + 273

15. A solid becoming a liquid is called: • Freezing • Melting • Evaporation • Sublimation • Condensation • Deposition

16. A gas becoming a liquid is called: • Freezing • Melting • Evaporation • Sublimation • Condensation • Deposition

17. A solid becoming a gas is called: • Freezing • Melting • Evaporation • Sublimation • Condensation • Deposition

18. A liquid becoming a gas is called: • Freezing • Melting • Evaporation • Sublimation • Condensation • Deposition

19. Attractive Forces • In gases, these attractive forces are minimal. • In solids and liquids, the forces are strong enough to keep the materials from scattering everywhere. • These attractive forces also determine the melting point and boiling point of different compounds. (ex. NaCl melts at 801o C)

20. Changes in State • Materials experience a change in state when enough heat energy is applied to break apart (or form) the attractions between molecules. • When intermolecular bonds are broken, heat is absorbed from the surroundings; when the bonds are formed, heat is taken from the system and released to the surroundings.

21. Changes in State • Different states of matter (solids, liquids, and gases) have very different properties due to attractive forces that exist between atoms. • To change from a solid to a liquid, for example, these attractive forces in solids must be broken so that the liquid molecules have more freedom to move. In gases, the molecules have even more mobility.

22. When a solid melts, heat is removed from the surrounding environment to break those intermolecular forces. • True • False

23. When a gas condenses, heat is removed from the surrounding environment? • True • False

26. What happens at B? • Solid starts to melt • Liquid starts to freeze • Gas starts to condense • Liquid starts to evaporate

27. What happens at D? • Solid starts to melt • Liquid starts to freeze • Gas starts to condense • Liquid starts to boil

28. What happens at E moving from right to left in the graph? • Solid starts to melt • Liquid starts to freeze • Gas starts to condense • Liquid starts to evaporate

29. What happens at C moving from right to left in the graph? • Solid starts to melt • Liquid starts to freeze • Gas starts to condense • Liquid starts to evaporate

30. Heating Curves

31. Melting Point / Freezing Point • The melting point (same temperature as freezing point) is the temperature at which a solid turns to a liquid. • Latent Heat of Fusion – the amount of heat needed to freeze one gram of a substance (or the heat released when one gram of a substance melts.) • Note: units in J/g

32. Latent Heat of Fusion Q = m x Hfus Heat = mass x Heat of Fusion ****For ice to water: Hfus = 334 J/g (every substance has a difference heat of fusion)

33. Boiling Point / Condensation Point • The boiling point (same temperature as condensation point) is the temperature at which a liquid turns to a gas. • Latent Heat of Vaporization – the amount of heat needed to vaporize one gram of a substance (or the heat release when one gram of a substance condenses.) • Note: units in J/g

34. Latent Heat of Vaporization Q = m x Hvap Heat = mass x Heat of Vaporization ****For water to steam: Hvap = 2260 J/g (every substance has a difference heat of vaporization)

36. Heat Graph calculations • When the graph is flat, use latent heat equations because of change of state. • For melting: Q = m x Hfus • For evaporating: Q = m x Hvap

37. Specific Heat • Different substances absorb (and lose) heat at different rates. • Specific heat (SH) is the amount of heat (q) needed to raise the temperature of 1 gram of a substance by 1 degree Celsius.

38. Heat Graph calculations • When the graph is sloped, use specific heat equations because of change of temperature • Q = SH x m x Temp. Change or

39. Measuring Heat Changes • A calorimeter is an instrument used to measure heat changes. By placing an object in an insulated container, the heat loss can be measured by the temperature gain of the water. Heat lost by object = Heat gained by water -qobject = qwater

40. Why do chemical reactions occur between some substances and not in others?

41. Chemical reactions occur so that the atoms in the elements involved attain a more stable state of being.

42. Collision Theory • Collision theory – molecules must collide with the proper orientation and sufficient energy to react.

44. Activation Energy • The activation energy is the amount of energy required to break the bonds between the atoms of the reactants.

46. Condition Necessary for Reactions to Occur • Collision: Reactants must collide. 2) Orientation: The reactants must align properly to react. 3) Energy: The activation energy must be attained to react.

47. Energy in Chemical Reactions • Many chemical reactions also produce energy changes. • Definitions: • System – the reactants and products in the reaction • Surroundings – everything else around the reaction (eg air in the room, reaction flask)

48. Heat of Reaction • Heat of Reaction (ΔH) – the amount of heat lost or gained in a reaction • Heat of Reaction: ΔH = Hproducts – Hreactants Hair products

49. Exothermic Reactions • Exothermic Reactions – energy is produced by a reaction; energy flows from the system to the surroundings • ΔH is negative because the reaction loses heat.

50. Exothermic Reaction Graph