Energy Chapter 16 Chapter 16

Energy: Ability to do Work Potential Energy (PE) = Energy of position aka STORED energy aka STORED energy Kinetic Energy (KE) = Energy of motion Radiant Energy = Electromagnetic radiation Ex: sunlight Ex: sunlight

Types of Energy (Not a complete list!)

Units of Energy  SI system - unit of energy is JOULE (J)  1 Joule ≅ amount of energy required to lift 1 golf ball about 1 meter lift 1 golf ball about 1 meter

other energy units: other energy units: calorie, Calorie, BTU calorie, Calorie, BTU 1 calorie = 4.18 Joules 1 calorie = 4.18 Joules 1 Calorie = 1000 calories = 1 kilocalorie 1 Calorie = 1000 calories = 1 kilocalorie

Kinetic Energy  KE = ½ x mass x velocity 2 = ½ mv 2  So KE of matter depends on: how heavy and how fast how heavy and how fast

Potential Energy  stapler  rubberband  popper  anything can have PE = energy of position = energy of position = stored energy = stored energy  PE can be converted to KE converted to KE

Magnets  PE in the system of 2 magnets depends on their relative position  when magnets get close together they will pull together due to attraction  when magnets are far apart they can’t attract each other

Electromagnetic Radiation  sunlight – Visible radiation  ultraviolet radiation  infrared radiation  gamma rays  x-rays  Microwaves  radiowaves Applet spectrum

Energy in Chemistry  chemical energy is energy stored within chemical bonds  heat: form of energy form of energy flows from warmer object to cooler object flows from warmer object to cooler object  (macroscopic)

Heat Energy  heat: energy associated with motion of energy associated with motion of atoms/molecules in matter atoms/molecules in matter  (microscopic)  symbol for heat energy = Q or q

Heat Energy  heat depends on amount of substance present  we can only measure heat changes

Temperature is measure of aver KE of particles in sub  swimming pool of water vs. glass of water  temperature is NOT energy TEMP does NOT depend on amount of substance TEMP does NOT depend on amount of substance ENERGY does depend on amount of substance ENERGY does depend on amount of substance

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 golf ball hit off tee - radiant to electric solar heat to electricity - electric to heat electric stove cooking food - chemical to kinetic burning charcoal on grill - chemical to electrical batteries creating electricity

All physical & chemical changes are accompanied by change in energy Thermochemistry: chemistry of energy changes

Energy Transfer  measure changes in heat  amount energy transferred from one substance to another one substance to another  can measure energy lost somewhere or energy gained somewhere else  cannot measure absolute heat content of system

Energy of Universe is conserved Universe Environment System Energy energy can move between system and environment

Exothermic Change  system releases heat to environment what happens to temperature of environment? what happens to temperature of environment?  EXO - energy leaves system (exits)  what happens to energy level of system? what happens to temperature of system? what happens to temperature of system? Environment System

Environment System Energy EXO - energy leaves system (exits) temperature of environment  temperature of system 

Exothermic Change  system: net energy loss!  environment: net energy gain!  energy lost = energy gained

Endothermic Change  system absorbs heat from environment what happens to temperature of environment? what happens to temperature of environment?  Endo - Energy enters system  what happens to energy level of system  what happens to temperature of system? Environment System

Endo - Energy enters system (entrance) Environment System Energy temperature of environment  temperature of system 

Endothermic Change  system - net energy gain!  environment - net energy loss!  energy lost = energy gained

Heat Flow  heat flows from hotter object to cooler object  cold pack on leg: heat flows from leg to cold pack! leg cools down; cold pack warms up leg cools down; cold pack warms up

Quantity of heat transferred  quantity (amount) of heat transferred depends on temperature change temperature change mass of substance mass of substance Specific heat of substance Specific heat of substance

Calculating Heat Transferred Q = mc  T simple system: pure substance in single phase calculate heat gained or lost using: Q = amount of heat transferred m = mass of substance c = specific heat capacity of the substance.  T = temperature change = T final – T initial

Specific Heat  amount heat energy required to raise temp of 1 gram of substance by 1 o C raise temp of 1 gram of substance by 1 o C  symbol = c  specific heat = a physical constant  unique for each pure substance

calorimeter: used to measure heat changes

source other examples

Calorimetry  changes in heat energy are measured by calorimetry  “universe” contained in styrofoam cup  “enviroment” is water****  “system” is whatever put in water

Calorimetry  energy lost = energy gained  difficult to monitor “system”  easy to monitor “environment” (water)  energy lost/gained by environment = energy gained/lost by system energy gained/lost by system

Calorimetry 10 grams of NaOH is dissolved in 100 g of water & the temperature of the water increases from 22  C to 30  C.  was dissolving process endothermic or exothermic how do you know? how do you know? exothermic – temperature of environment ↑

Dissolving  What’s happening when NaOH dissolves? Add H 2 O molecules close together, not interacting molecules pulled apart & interacting with H 2 O

Calorimetry calculate energy released by NaOH as it dissolves in water calculate energy released by NaOH as it dissolves in water energy lost by NaOH = energy gained by water easier to calculate from H 2 O perspectiveeasier to calculate from H 2 O perspective Q = mc  T Q = energy (joules) m = mass (grams) c = specific heat capacity (Table B)  T = temperature change = T f - T i

Calorimetry & Q = mC  T  temperature of water increased from 22  C to 30  C  what mass to use? temp change was for water, so use mass H 2 O  same goes for specific heat capacity; calculate heat absorbed by water 30  C -22  C = 8  C =  T m= 100 g C H 2 0 = 4.18J/g  C

Q = mc  T  Q = (100 g)(4.18 _J )(8  C) g  C g  C  Q = 3344 J

Stability and Energy  if energy is high, stability is low  if energy is low, stability is high