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What is energy? • The ability to do work • The ability to transfer heat Two types: Potential and Kinetic Page 2
Potential Energy • Stored Energy • Energy due to • Position • Chemical Bonds • Nuclear • Position: boulder at the top of the hill • Chemical: tank of gas, hamburger • Nuclear: atomic bomb, nuclear reactor
Kinetic Energy • Active Energy • Energy of Motion • Electromagnetic waves, (ex. Light, Xrays) • Heat • Motion • Electrical current, • A moving truck has the ability to flatten you - do work on you!
First Law of Thermodynamics • Energy can neither be created nor destroyed, but may change from one form to another. Page 2 bottom
Entropy – 2nd Law • Entropy is the amount of disorder in a system • Entropy always increases over time (in the absence of an input of outside energy) • Example: cleaning up your room
Chemical OR Physical changes can be exothermic or endothermic.
Regents Question: 06/02 #64-66 • A hot pack contains chemicals that can be activated to produce heat. A cold pack contains chemicals that feel cold when activated. • Based on energy flow, state the type of chemical change that occurs in a hot pack. • Exothermic • A cold pack is placed on an injured leg. Indicate the direction of the flow of energy between the leg and the cold pack. • From the leg to the cold pack (Hot to Cold) • What is the Law of Conservation of Energy? Describe how the Law of Conservation of Energy applies to the chemical reaction that occurs in the hot pack. • Energy cannot be created nor destroyed. It can only be changed from one form to another. The heat produced in the hot pack was stored in the chemical bonds.
Page 5 Measuring Energy
Energy • There are two units which are commonly used: • Calories (c): • amount of energy it takes to raise one gram of water one degree Celsius • Joules (J): • 4.18 Joules = 1 calorie • Metric system is most commonly used in chemistry
Page 6 • Converting between Celsius and Kelvin • Reference Table • Why is it not out already? • Temperature Towards bottom K = ◦C + 273
Heat and Temperature • Temperature measures the average speed of the atoms • Heat is the amount of kinetic energy of the atoms
Phases of Matter- Page 9 Ice Ice Ice Regular Irregular Irregular Regular Irregular Regular Minimal Moderate Fast
Graph page 11 onto page 13. Be sure to have an appropriate scale. Circle the points and connect them.
F D E B C A
A change in phase is a change in Potential Energy, not Kinetic Energy Boiling Point Potential energy changes, so temperature doesn’t Melting Point
Energy and phase changes • AB • solid warms up (KE/PE constant)
Energy and phase changes • AB • solid warms up (KE/PE constant) • BC • solid melts (KE constant/PE)
Energy and phase changes • AB • solid warms up (KE/PE constant) • BC • solid melts (KE constant/PE) • CD • liquid warms up (KE/PE constant)
Energy and phase changes • AB • solid warms up (KE/PE constant) • BC • solid melts (KE constant/PE) • CD • liquid warms up (KE/PE constant) • DE • liquid boils (KE constant/PE)
Energy and phase changes • AB • solid warms up (KE/PE constant) • BC • solid melts (KE constant/PE) • CD • liquid warms up (KE/PE constant) • DE • liquid boils (KE constant/PE) • EF • gas warms (KE/PE constant)
Regents Question: 06/02 #28 As ice melts at standard pressure, its temperature remains at 0°C until it has completely melted. Its potential energy (1) decreases (2) increases (3) remains the same þ
Phase change Gas Only Liquid Only Regents Question: 08/02 #54 A sample of water is heated from a liquid at 40°C to a gas at 110°C. The graph of the heating curve is shown in your answer booklet. a On the heating curve diagram provided in your answer booklet, label each of the following regions: Liquid, only Gas, only Phase change
Regents Question: cont’d b For section QR of the graph, state what is happening to the water molecules as heat is added. c For section RS of the graph, state what is happening to the water molecules as heat is added. They move faster, their temperature increases. Their intermolecular bonds are breaking, their potential energy is increasing.
Regents Question: 01/02 #47 What is the melting point of this substance? (1) 30°C (3) 90°C (2) 55°C (4) 120°C þ
Graph page 14 onto page 16. Be sure to have an appropriate scale. Circle the points and connect them.
A B C D E F
Energy and phase changes • AB • Gas cools down (KE/PE constant) • BC • Gas condenses (KE constant/PE ) • CD • liquid cools down (KE /PE constant) • DE • liquid freezes (KE constant/PE ) • EF • Solid cools down(KE /PE constant)
Page 19 How do we calculate amount of heat,(Q), if we are not given a graphic?