Energy Chapter 16

Energy: Ability to do Work Potential Energy = Energy of position Also called STORED ENERGY Kinetic Energy = Energy of motion Radiant Energy = Electromagnetic Ex: Sunlight

Types of Energy (Not a complete list!)

Units of Energy SI system - unit of energy is JOULE (J) 1 Joule = amount energy required to lift 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 = ½ x Mass x Velocity2 = ½ mV2 So KE depends on: how heavy how fast

Potential Energy Kleenex Box Spring Rubberband Popper Anything can have PE = energy of position = stored energy PE can be converted to KE

Magnets 2 magnets: PE depends on relative position

Electromagnetic Radiation Sunlight – Visible radiation Ultraviolet radiation Infrared radiation Gamma rays X-rays Microwaves Radiowaves Applet spectrum

Energy in Chemistry Chemical energy = energy stored in bonds Heat = form energy that flows from warmer object to cooler object (Macroscopic)

Heat Energy Heat: energy associated with motion of atoms & molecules in matter (Microscopic) Symbol for heat energy = Q or q

Heat Energy Heat depends on amount of substance present measure changes in heat

Temperature measure of average KE 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 and chemical changes are accompanied by energy changes chemistry of energy changes = Thermochemistry!

Energy Transfer Measure changes in heat amount energy transferred from one substance to another measure energy lost somewhere or energy gained somewhere else Cannot measure absolute heat content

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

Exothermic Change System releases heat to environment EXO - energy leaves system (exits)

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

Exothermic Change System has net loss in energy! Environment has net gain in energy! Energy lost = Energy gained

Endothermic Change System absorbs heat from environment Endo - Energy enters system

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

Endothermic Change System has net gain in energy! Environment has net loss in energy! 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

Quantity of heat transferred Quantity (amount) of heat transferred depends on Temperature change Mass of substance Specific Heat of substance

Calculating Heat Transferred Q = mCT 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 1 oC 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 The “universe” is contained in a styrofoam cup The “enviroment” is the water**** The “system” is whatever is 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

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 the dissolving process endothermic or exothermic how do you know? Exothermic – the temperature of the environment increased

Dissolving What’s happening when the NaOH dissolves? Add H2O molecules close together, not interacting molecules pulled apart & interacting with H2O

Calorimetry Q = mCT Q = energy (joules) M = mass (grams) Calculate energy released by NaOH in previous problem as it dissolved in water Energy lost by NaOH = Energy gained by water Easier to calculate from H2O perspective Q = mCT Q = energy (joules) M = mass (grams) C = specific heat capacity (Table B) T = temperature change = Tf - Ti

Calorimetry & Q = mCT temperature of water increased from 22C to 30C 30C -22C = 8C = T What mass to use? Well, temp change was for water, so use mass of water m = 100 g Same goes for specific heat capacity; calculate heat absorbed by water cH20 = 4.18J/g C

Q = mCT Q = (100 g)(4.18 J/g)(8C) Q = 3344 Joules

Stability and Energy If energy is high, stability is low If energy is low, stability is high