Energy

1. Energy Energy is defined as the ability to do work. Work = force x distance

2. Energy The ability to do work. • Work - cause a change or move an object. • Many types- all can be changed into the other.

3. Types of energy • Potential- stored energy • Position, condition or composition • Kinetic Energy- energy something has because its moving • Heat- the energy that moves because of a temperature difference. • Chemical energy- energy released or absorbed in a chemical change. • Electrical energy - energy of moving charges

4. Types of Energy con’t • Radiant Energy- energy that can travel through empty space (light, UV, infrared, radio) • Nuclear Energy – Energy from changing the nucleus of atoms *All types of energy can be converted into others. • If you trace the source far enough back, you will end up at nuclear energy.

5. Conservation of Energy Energy can be neither created or destroyed in ordinary changes (not nuclear), it can only change form. • Discovered by Julius Robert Mayer in 1842 • Now called: The First Law of Thermodynamics Law of Conservation of Mass - Energy The total amount of mass and energy in the universe is constant.

6. The kinetic molecular theory is useful in describing thermal energy, heat, and temperature. • Some theories are based on supporting postulates. • A postulate is a statement which is agreed on by consensus among scientists. • The following are important postulates of the kinetic molecular theory:

7. All matter consists of atoms. • Atoms may join together to form molecules. • Solids usually maintain both their shape and their volume. • Liquids maintain their volume, but not their shape. • Gases do not maintain shape or volume. They will expand to fill a container of any size. • Molecular motion is random. • Molecular motion is greatest in gases, less in liquids, and least in solids. • Collisions between atoms and molecules transfers energy between them. • Molecules in motion possess kinetic energy. • Molecules in gases do not exert large forces on one another, unless they are colliding. • Also see chapter 11 of textbook Kinetic Molecular Theory

8. Thermal energyis the average of the potential and kinetic energies possessed by atoms and molecules experiencing random motion. • Heat is transferred by convection, conduction, or radiation. (review the definitions of these words) • Heat is the thermal energy transferred from one object to another due to differences in temperature. Heat flow from high to low temperature.

9. There is no direct method used to measure heat. Indirect methods must be used. Temperature is a measure of the average kinetic energy of the molecules of a substance. • There is a direct relationship between temperature and avg. kinetic energy! • Temperature can be measured with a thermometer.

10. One way a thermometer can be calibrated is by the amount of thermal expansion and contraction that occurs within a given type of substance. • Thermometers are limited by the physical properties of the substance from which they are made. (i.e., An alcohol thermometer is of little use above the boiling point of alcohol, and a mercury thermometer will not be of any use below the freezing point of mercury.)

11. What's the difference between the Fahrenheit and Celsius temperature scales? • Both scales are based on the freezing conditions of water, a very common and available liquid. • Since water freezes and boils at temperatures that are rather easy to generate (even before modern refrigeration), it is the most likely substance on which to base a temperature scale.

12. 100ºC = 212ºF 0ºC = 32ºF 100ºC 212ºF 32ºF 0ºC

13. Zero Fahrenheit was the coldest temperature that the German-born scientist Gabriel Daniel Fahrenheit could create with a mixture of ice and ordinary salt. • He invented the mercury thermometer and introduced it and his scale in 1714 in Holland, where he lived most of his life.

14. Anders Celsius, a Swedish astronomer, introduced his scale is 1742. • For it, he used the freezing point of water as zero and the boiling point as 100. • For a long time, the Celsius scale was called "centigrade." • The Greek prefix "centi" means one-hundredth and each degree Celsius is one-hundredth of the way between the temperatures of freezing and boiling for water. • The Celsius temperature scale is part of the "metric system" of measurement (SI) and is used throughout the world, though not yet embraced by the American public.

15. How much it changes 100ºC = 212ºF 0ºC = 32ºF 100ºC = 180ºF 0ºC 100ºC 212ºF 32ºF

16. How much it changes 100ºC = 212ºF 0ºC = 32ºF 100ºC = 180ºF 1ºC = (180/100)ºF 1ºC = 9/5ºF 0ºC 100ºC 212ºF 32ºF

17. Scientists use a third scale, called the "absolute" or Kelvin scale. • This scale was invented by William Thomson, Lord Kelvin, a British scientist who made important discoveries about heat in the 1800's. • Scientists have determined that the coldest it can get (theoretically) is minus 273.15 degrees Celsius. • This temperature has never actually been reached, though scientists have come close. The value, minus 273.15 degrees Celsius, is called "absolute zero". • At this temperature scientists believe that molecular motion would stop. You can't get any colder than that. • The Kelvin scale uses this number as zero. To get other temperatures in the Kelvin scale, you add 273 degrees to the Celsius temperature.

18. The important idea is that temperature is really a measure of something, the average motion (kinetic energy, KE) of the molecules. KE = ½ mv2 • Does 0°C really mean 0 KE? nope... it simply means the freezing point of water, a convenient standard. • We have to cool things down to –273.15°C before we reach 0 KE. This is called 0 Kelvin (0 K, note: NO ° symbol.) • For phenomena that are proportional to the KE of the particles (pressure of a gas, etc.) you must use temperatures in K.

19. Temperature Conversion • K = °C + 273 • °C = K – 273 • °F = 9/5 °C + 32 • °C = 5/9 (°F – 32) Note: In Kelvin notation, the degree sign is omitted: 283K

20. Celsius to Fahrenheit: *A mental shortcut for a rough estimate: · Double the temperature given in Celsius · Add 30 to the result to find the approximate temperature in Fahrenheit.

21. Celsius Temperature to Fahrenheit More Celsius to Fahrenheit Fahrenheit to Celsius More Fahrenheit to Celsius

22. Fahrenheit to Celsius: *A mental shortcut for a rough estimate: ·Subtract 30 from the temperature given in Fahrenheit · Take half of the result to find the approximate temperature in Celsius.

23. Celsius Temperature to Fahrenheit More Celsius to Fahrenheit Fahrenheit to Celsius More Fahrenheit to Celsius

24. How Do We Measure Energy? Energy is measured in many ways. BTU • One of the basic measuring blocks is called a Btu. This stands for British thermal unit and was invented by the English. • Btu is the amount of heat energy it takes to raise the temperature of one pound of water by one degree Fahrenheit, at sea level. • One Btu equals about one blue-tip kitchen match. • One thousand Btus roughly equals: One average candy bar or 4/5 of a peanut butter and jelly sandwich. • It takes about 2,000 Btus to make a pot of coffee.

25. Calorie • A calorie is a unit of measurement for energy. • Calorie is a French word derived from the Latin word: calor (heat). Modern definitions for calorie fall into two classes: • The small calorie or gram calorie approximates the energy needed to increase the temperature of 1 gram of water by 1 °C. This is about 4.184 joules. • The large calorie or kilogram calorie approximates the energy needed to increase the temperature of 1 kg of water by 1 °C. This is about 4.184 kJ, and exactly 1000 small calories. • 1 cal = 4.184 J

26. Joule • Energy also can be measured in joules. (Joules sounds exactly like the word jewels, as in diamonds and emeralds.) • A thousand joules is equal to a British thermal unit. • 1,000 joules = 1 Btu • So, it would take 2 million joules to make a pot of coffee.

27. The term "joule" is named after an English scientist James Prescott Joule who lived from 1818 to 1889. • He discovered that heat is a type of energy. • One joule is the amount of energy needed to lift something weighing one pound to a height of nine inches. • Around the world, scientists measure energy in j.

28. Like in the metric system, you can have kilojoules -- "kilo" means 1,000. • 1,000 joules = 1 kilojoule = 1 Btu • 1 cal = 4.184 J

29. Kinetic Energy and Temperature • Temperature is a measure of the Average kinetic energy of the molecules of a substance. • Higher temperature faster molecules. • At absolute zero (0 K) all molecular motion would stop.

30. High temp. % of Molecules Low temp. • Kinetic Energy

31. High temp. % of Molecules Low temp. Average kinetic energies are temperatures • Kinetic Energy

32. Temperature • The average kinetic energy is directly proportional to the temperature in Kelvin • If you double the temperature (in Kelvin) you double the average kinetic energy. • If you change the temperature from 300 K to 600 K the kinetic energy doubles.

33. Temperature • If you change the temperature from 300ºC to 600ºC the Kinetic energy doesn’t double. • 873 K is not twice 573 K

34. Melting Vaporization Freezing Condensation Phase Changes Solid Gas Liquid

35. Sublimation Vaporization Deposition endothermic Melting Solid Gas Liquid Freezing Condensation exothermic

36. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800

37. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 gas liquid Slope = Specific Heat Solid

38. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Both Solid and liquid

39. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Both liquid and gas

40. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Heat of Vaporization

41. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Heat of Fusion

42. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800 Plateau = phase equilibrium

43. Energy and phase changes

44. Heat is transferred to different materials at different rates. • The specific heat capacity (Cp) determines the rate at which heat will be absorbed. • Even though mass is present in the formula it is an intensive property like density and is unique for each substance. • The specific heat capacity for water Cp is 4.184 J/g • The quantity of heat absorbed (Q) can be calculated by: Q=m Cp T m=mass T=change in temperature

45. Note the tremendous difference in Specific Heat. Water’s value is VERY HIGH.

46. Heat Capacity Heat capacity is an extensive property, meaning it depends on the mass of the object. Ex: 1000g of water can hold more heat than 10 g of water.

47. Calculating Energy Q means heat energy lost or gained. (units are calories or joules) Law of Conservation of Mass-Energy m= mass of substance; Cp= specific heat capacity; DT = change in temperature Qlost = Qgained Three equations: • Q= mass x Cp x DT • Q= Hf x mass • Q= Hv x mass

48. Heating Curve for Water 120 Steam Water and Steam 100 80 60 Water 40 20 Water and Ice 0 Ice -20 40 120 0 220 760 800

49. Energy and Phase Change • Heat of fusion energy required to change one gram of a substance from solid to liquid. (endothermic rxn) • Heat of solidification (crystallazation or freezing)energy released when one gram of a substance changes from liquid to solid. (exothermic rxn) • For liquid water 80 cal/g or 334 J/g

50. Energy and Phase Change • Heat of vaporization energy required to change one gram of a substance from liquid to gas. (endothermic rxn) • Heat of condensation energy released when one gram of a substance changes from gas to liquid. (exothermic rxn) • For water 540 cal/g or 2260 J/g