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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! Kinetic and Potential Energy Electromagnetic Spectrum First Law of Thermodynamics Energy can neither be created nor destroyed, but may change from one form to another. Page 2 bottom Entropy – nd 2 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 Page 3 Page 4 Exothermic vs Endothermic Chemical OR Physical changes can be exothermic or endothermic. Endothermic Exothermic Definition Stored energy Energy of motion Energy is Absorbed Released Temperature +∆H Chemical -∆T Physical +∆T -∆H Chemical +∆T Physical -∆T 2H2O + energy 2H2 + O2 Energy is on the left 2H2 + O2 2H2O + energy Energy is on the right Type of Energy Conversion Example 12 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. 1. Based on energy flow, state the type of chemical change that occurs in a hot pack. Exothermic 2. 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) 3. 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. 14 Page 5 Measuring Energy I. Energy A. There are two units which are commonly used: B. Calories (c): 1. amount of energy it takes to raise one gram of water one degree Celsius C. Joules (J): 1. 4.18 Joules = 1 calorie 2. Metric system is most commonly used in chemistry Criteria Heat Temperature Similar/Different Energy Kinetic Motion of Molecules Both are about Motion Quantitative Aspect How fast molecules are moving. Measured by temperature Kelvin and Celsius A form of Kinetic Energy that involves movement of molecules The measurement of how fast a molecule is moving Definition Examples Celsius based on properties of water Kelvin based on Celsius Temperature is a measurement of Kinetic Energy Page 6 III. Converting between Celsius and Kelvin A. Reference Table B. Why is it not out already? 1. 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 Page 7 To convert between Kelvin and Celsius use ◦ K= C+273 J Deutsch 2003 21 Page 8 Phases of Matter- Page 9 Ice Ice Ice Regular Irregular Irregular Regular Regular Irregular Minimal Moderate Fast Page 10 Graph page 11 onto page 13. Be sure to have an appropriate scale. Circle the points and connect them. Heating Curve 180 F 160 140 120 D E 100 80 60 B C 40 20 A 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 A change in phase is a change in Potential Energy, not Kinetic Energy Boiling Point Potential energy changes, so temperature doesn’t Melting Point 28 Energy and phase changes AB solid warms up (KE/PE constant) 30 Energy and phase changes AB solid warms up (KE/PE constant) BC solid melts (KE constant/PE) 32 Energy and phase changes AB solid warms up (KE/PE constant) BC solid melts (KE constant/PE) CD liquid warms up (KE/PE constant) 34 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) 36 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) 38 J Deutsch 2003 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 40 J Deutsch 2003 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 Phase change Gas Only Liquid Only 41 J Deutsch 2003 Regents Question: cont’d b For section QR of the graph, state what is happening to the water molecules as heat is added. They move faster, their temperature increases. c For section RS of the graph, state what is happening to the water Their intermolecular bonds molecules as heat is added. are breaking, their potential energy is increasing. 42 J Deutsch 2003 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 43 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) 46 Pages 17-18 Page 19 How do we calculate amount of heat,(Q), if we are not given a graphic? 3 equations for Q Q = mCT Q = mHf Q = mHv Have to figure out which one to use for a given problem. Depends which section of heating curve. Look for hints in the problem. Calculating Heat Transferred Simple system: Pure substance in a single phase. To calculate heat gained or lost, use: Q = mCT •Q = amount of heat transferred •m = mass of substance •C = specific heat capacity of the substance (Table B). •T = temperature change = Tfinal – Tinitial Q = mCT Temperature changed Temperature increased Temperature decreased Initial / Start temperature Final temperature Ending temperature From ____ to ____ Water Amount of energy required to convert 1 gram of a pure substance from the solid to the liquid phase at the melting point. Heat of Fusion Q = mHf Use this equation to calculate energy changes for phase changes between ice & liquid water at 0C. Q = mHf Ice Freezing Melting At 0C (for H2O) At constant temperature Amount of energy required to convert 1 gram of a pure substance from the liquid to the gas phase at the boiling point. Heat of Vaporization Q = mHv Use this equation to calculate energy changes for phase changes between steam & liquid water at 100C. Q = mHv Steam Boiling Condensation At 100C (for H2O) At constant temperature