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

Some 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 (cal) calorie (cal) Calorie (Cal) Calorie (Cal) british thermal units (BTU) british thermal units (BTU) 1 calorie = 4.18 Joules 1 Calorie = 1000 cal = 1 kilocalorie = 4180J

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

Energy in Chemistry chemical energy: energy stored within chemical bonds between atoms  heat: form of energy form of energy flows from warmer object to cooler object flows from warmer object to cooler object

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

Heat Energy  heat depends on amount of substance present  can only measure changes in heat energy not absolute value of heat energy not absolute value of heat energy

Temperature measure of average KE of particles in sub  temperature is NOT energy  temperature is NOT energy  TEMP does NOT depend on amount  TEMP does NOT depend on amount  ENERGY does !  ENERGY does !

Law of Conservation of Energy  energy is neither created nor destroyed in ordinary chemical or physical change  reminder: nuclear rxn a small amount of mass is converted to energy energy before = energy after

Energy can be converted from one form to another Energy can be converted from one form to another

 potential to kinetic  radiant to electric  electric to heat  chemical to kinetic  chemical to electrical golf ball hit off tee solar heat to electricity electric stove cooking food burning charcoal on grill 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)  measure energy lost somewhere or or energy gained somewhere else energy gained somewhere else

energy of universe is conserved universe (room) Environment environment (container) system (substances) energy energy can move between system and environment (goes in or out)

EXothermic Change  system releases heat to environment what happens to temperature of environment? what happens to temperature of environment?  EXo - heat is EXiting what happens to temperature of system? what happens to temperature of system? environment system temperature of system  temperature of environment  what happens to energy level of system? ↓

Exothermic Change energy lost = energy gained energy lost = energy gained (system) (environment) (system) (environment)

Endothermic Change  system absorbs heat from environment what happens to temperature of environment? what happens to temperature of environment?  ENdo - heat ENters system what happens to temperature of system? what happens to temperature of system? environment system temperature of environment  temperature of system  what happens to energy level of system? ↑

Endothermic Change energy lost = energy gained energy lost = energy gained (environment) (system) (environment) (system)

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

Calorimetry  changes in heat energy are measured using calorimeter (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

calorimeter: used to measure heat changes “universe” = styrofoam cup “enviroment” = water**** “system” is whatever put in water (reactants)

 quantity (amount) of heat transferred depends on: amount temperature change amount 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  see Table B for water (4.18J/g˚C)

typical word problem 10 grams of NaOH(s) is dissolved in 100 g of water & the temperature of the water increases from 22  C to 30  C.  dissolving process: was it endothermic or exothermic? was it endothermic or exothermic? how do you know? how do you know? temperature ↑ exothermic

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

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