1	CHAPTER 10 ENERGY
2	10.1 The Nature of Energy The usual definition of energy: the ability to do work Work is moving an object against an opposing force Work = distance × opposing force [ w = d x f ] SI unit of work or energy: the joule (J)
3	A joule A joule is the mechanical equivalent of heat meaning the number of units of work which the unit of heat can perform. Its value was found by James Prescott Joule in experiments that showed the mechanical energy which must be expended to raise the temperature of a unit weight of water by 1 degree F. was equivalent to 772 foot-pounds upon the Fahrenheit, thermometric scale, by reason of which it is often called Joule's equivalent, and represented by the symbol J.
4	Two basic types of energy Potential Energy: energy of position Examples Boulder on a ledge Cations and anions Chemical bonds Tell how each of the examples above have potential energy.
5	Two basic types of energy Kinetic Energy: energy of motion. It depends on the mass and velocity of the object. KE = ½ mv² (where m = mass and v = velocity) Examples Pool balls Molecules How do each of these have kinetic energy?
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7	"Chemical Energy - stored energy..." Chemical Energy - stored energy that depends on the composition of the substance. Food and gasoline Nuclear Energy - energy involved in nuclear reactions. Electrical Energy - the chemical reaction that occurs in the battery of a car produces electrical energy used to start the car and operate the headlights, radio, etc.
8	There are several forms of energy Light Energy - plants use the radiant energy of sunlight to do the work of making carbon dioxide and water into sugar. This process of creating stored chemical energy is photosynthesis. Mechanical energy – used to do mechanical work Sound Energy Thermal Energy – heat Two things energy is NOT Some sort of invisible fluid Something which can be measured directly
9	"Energy can be converted from..." Energy can be converted from one form to another form which is more useful. This occurs all around you on a daily basis. Example: Consider when electrical energy is converted into heat energy in a hair dryer. Give another example of energy conversion
10	"A fundamental law governs these..." A fundamental law governs these energy conversions:
11	Law of Conservation of Energy in any chemical or physical change, energy is neither created nor destroyed. (which other law does this remind you of?) Energy may be converted from one form to another but it is always conserved. All the energy involved can be accounted for as work, stored energy, or heat.
12	10.2 Temperature and Heat Thermal energy Definition: energy due to chaotic molecular motions Three factors affecting thermal energy Temperature – Definition: a measure of the random motion of the components (atoms/molecules) of a substance Higher temperature leads to higher thermal energy Sample size A cup of hot coffee has more energy than a teaspoon of coffee, all other things being equal. Composition E (solid) < E (liquid) < E (gas), all other things being equal
13	Heat Anything that changes temperature, sample size and/or composition of an object can change its thermal energy Heat Definition: transfer of thermal energy due to a temperature difference Thermal energy isn't measurable, but heat is
14	Molecular logic time!! Fill in the worksheet as we go through the animations together…
15	10.3 Exothermic and Endothermic Processes According to chemistry/physics, when studying reactions etc… the universe is divided into 2 parts: The System: the part of the universe which you focus your attention. The Surroundings: everything else in the universe.
16	Exothermic reaction Energy is lost to the surroundings as heat What examples can you think of? Think of it in terms of motion of particles
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18	Endothermic reaction Energy is absorbed from the surroundings What examples can you think of? Consider this: If a chemical reaction gives off heat is it endothermic or exothermic?
19	Practice: Are the following examples of endothermic reactions or exothermic? Water freezing Ice melting Methane burning Water boiling
20	10.4 Thermodynamics Thermodynamics: The study of energy. The Law of conservation of energy is also called the First Law of Thermodynamics: The energy of the universe is constant
21	"When we study the heat..." When we study the heat involved in physical and chemical changes there will be two important factors: Amount of heat involved (number) Direction of heat flow (sign) Endothermic change - heat absorbed from the surroundings (q = +) Exothermic change - heat released to the surroundings (q = -)
22	To determine the change in energy of a system: DE = q + w where E is the amount of energy q represents heat w represents work
23	10.5 Measuring Energy Changes Thermal energy isn't measurable, but heat is. Measuring Heat involves these units. Calorie and Joule Calorie: the amount of energy required to raise the temperature of one gram of water one degree Celsius. calorie and Calorie are different. Calorie = 1000 calories. As on food labels
24	"Joule can be converted to..." Joule can be converted to calories 1 calorie = 4.184 joules convert 60.1 cal into joules 251J convert 34.8 cal into joules 146J convert 47.3J into cal 11
25	Three factors affect how much heat an object absorbs or loses 1. Mass of object 2. Temperature change of object Final temperature minus initial temperature If there is no change in temperature, no heat flows
26	"3." 3. Composition of object Specific heat: energy required to raise the temperature of 1 g of material by 1 Celsius Every substance has a specific heat that is unique to itself. The specific heat of water, for example, is 4186 J/ kg x °C (see table on page 297)
27	"Specific Heat Capacity is used..." Specific Heat Capacity is used to calculate temperature changes when a substance is heated Q = m ▪ Cp ▪ ΔT Q or q = Heat Energy in Joules m = mass in kilograms ΔT = change in temperature (Celsius) Cp or s = specific heat unit: joule/ kg x C
28	"Example:" Example: How much heat energy is absorbed when 88.0 grams of water is heated from 5.00 degrees Celsius to 37.0 degrees Celsius? ( c-H2O = 4186 J/ kg x C) Take inventory first: m = 0.0880 kg ( you must divide by 1000 to convert to kilograms) c = 4186 J / kg x C ΔT = 32 degrees Celsius ( 37 - 5 = 32) Q = ? Q = ( 0.0880)( 4186)(32) Q = 1.18 x 104 J
29	Try these examples 100.0 g of water-cools from 30.10°C to 25.05 °C. How much heat is released? 100.0 g of water at 25.00 °C absorbs 100 J of heat. What is its final temperature? A stone weighing 2.0 g absorbs 5.0 J of heat and warms by 3.0 °C. What is the specific heat of the stone? What is the heat capacity of the stone?