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Energy Chapter 16 Energy: Ability to do Work Potential Energy = Energy of position AKA STORED ENERGY Kinetic Energy = Energy of motion Radiant Energy = Electromagnetic Ex: Sunlight Types of Energy Energy Mechanical Kinetic Potential (Not a complete list!) Non-mechanical Chemical Electrical Magnetic Radiant Units of Energy SI system - unit of energy is the JOULE (J) 1 Joule = amount of energy required to lift a golf ball 1 meter Other Energy Units: calorie, Calorie, BTU’s 1 calorie = 4.18 Joules 1 Calorie = 1000 calories = 1 kilocalorie Kinetic Energy KE So = ½ x Mass x Velocity2 = ½ mV2 KE depends on how heavy and how fast Potential Energy stapler Rubberband Popper Anything can have PE = energy of position = stored energy Potential Energy can be converted to Kinetic Energy Magnets The potential energy in the system of 2 magnets depends on their relative position Electromagnetic Radiation Sunlight – Visible radiation Ultraviolet radiation Infrared radiation Gamma rays X-rays Microwaves Radiowaves Applet spectrum Energy in Chemistry Chemical bonds energy = energy stored in Heat – form of energy that flows from warmer object to cooler object (Macroscopic) Heat Energy Heat: energy associated with the motion of atoms & molecules in matter (Microscopic) Symbol for heat energy = Q or q Heat Energy Heat depends on amount of substance present We measure heat changes Temperature = measure of average kinetic energy of particles of substance Swimming Pool vs. Mug Temperature is NOT energy Temperature does NOT depend on amount of substance; energy does Law of Conservation of Energy Energy is neither created nor destroyed in ordinary chemical or physical change Energy before = Energy after Energy can be converted from one form to another - potential to kinetic - radiant to electric - electric to heat - chemical to kinetic - chemical to electrical All physical & chemical changes are accompanied by change in energy The chemistry of energy changes is known as Thermochemistry! Energy Transfer Measure changes in heat amount of energy transferred from one substance to another You can measure energy lost somewhere or the energy gained somewhere else Cannot measure absolute heat content of system Energy of Universe is conserved Universe EnvironmentEnvironment System Energy Energy can move between the system and the environment Exothermic Change System releases heat to environment What happens to the temperature of the environment? EXO - energy leaves system (exits) What happens to the energy level of the system? What happens to temperature of system? EXO - energy leaves system (exits) Temperature of environment Environment Temperature of system System Energy Exothermic Change System has net energy loss! Environment has net energy gain! Energy lost = Energy gained Endothermic Change System absorbs heat from environment What happens to temperature of environment? Endo - Energy enters system What happens to the energy level of the system? What happens to temperature of system? Endo - Energy enters system (entrance) Temperature of environment Environment System Energy Temperature of system Endothermic Change System has net energy gain! Environment has net energy loss! Energy lost = Energy gained Heat Flow Heat flows from hotter object to cooler object Cold pack on leg: Heat flows from the leg to the cold pack! Leg cools down; cold pack warms up Quantity of heat transferred Quantity (amount) of heat transferred depends on Temperature change Mass of substance Specific Heat of substance Calculating Heat Transferred Simple system: •pure substance in a single phase •calculate heat gained or lost using: Q = mCT Q = amount of heat transferred m = mass of substance C = specific heat capacity of the substance. T = temperature change = Tfinal – Tinitial Specific Heat Amount heat energy required to raise temp of 1 gram of substance by 1oC Symbol =c Specific heat = a physical constant Different for each pure substance Calorimeter Another example source Calorimetry Changes in heat energy are measured by calorimetry “universe” is contained in styrofoam cup “enviroment” “system” water is water**** is whatever we put in the Calorimetry Energy lost = Energy gained Difficult to monitor “system” Easy to monitor “environment” (water) Energy lost/gained by environment = Energy gained/lost by system Calorimetry 10 grams of NaOH is dissolved in 100 g of water & the temperature of the water increases from 22C to 30C was dissolving process endothermic or exothermic how do you know? Exothermic – temperature of environment ↑ Dissolving What’s happening when NaOH dissolves? Add H2O molecules close together, not interacting molecules pulled apart & interacting with H2O Calorimetry Calculate energy released by NaOH as it dissolved in water Energy lost by NaOH = Energy gained by water Easier to calculate from H2O perspective Q = mCT Q = energy (joules) M = mass (grams) C = specific heat capacity (Table B) T = temperature change = Tf - Ti Calorimetry & Q = mCT temperature 22C to 30C 30C What of water increased from -22C = 8C = T mass to use? Well, temp change was for water, so want mass of water m = 100 g Same goes for specific heat capacity; calculate heat absorbed by water cH 0 = 4.18J/g 2 Q = mCT Q = (100 g)(4.18 J/g)(8C) Q = 3344 Joules Stability and Energy If energy is high, stability is low If energy is low, stability is high