Energy Chapter 16, pages 489 to 505

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

Types of Energy (Not a complete list!)

Units of Energy IIIIn the SI system, the unit of energy is the JOULE. (J) 1111 Joule = amount of energy required to lift a golf ball 1 meter. OOOOther Units: calorie, Calorie, BTU’s 1111 calorie = 4.18 Joules 1111 Calorie = 1000 calories = 1 kilocalorie

Kinetic Energy  K.E. = ½ X Mass X Velocity 2 = ½ mV 2  So K.E. depends on how heavy and how fast.

Potential Energy  Kleenex Box  Spring  Rubberband  Popper  All these can have P.E. = energy of position = stored energy  Potential Energy can be converted to Kinetic Energy

Magnets Now hold the two magnets close enough to feel them attract each other, and then let go. When do they have the most potential energy? Hold two magnets close enough to feel them repel, then let them push apart. When do they have the most potential energy?

Magnets  The potential energy in the system of 2 magnets depends on their relative position.

Charge  The potential energy in the system of 2 charges depends on their relative position. (How far apart they are.)  Depends on the size of the charges, and the signs.

Charge: Electrostatics  Static0.mov Science 8 lab Static0.mov  Static1.mov Deflection of water Static1.mov  Static2.mov Close-up of water Static2.mov  Static3.mov Deflection of ethanol Static3.mov  Static6.mov Nonpolar CCl 4 Static6.mov  Static7.mov Animation of CCl 4 Static7.mov  Static8.mov Nonpolar Hexane Static8.mov Volume 1, CCA

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 – a form of energy that flows from a warmer object to a 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 the amount of substance present.  We measure changes in heat.

Temperature  A measure of the average kinetic energy of the particles of a substance.  Swimming Pool vs. Teacup  Temperature is NOT energy. Temperature does not depend on amount of substance; energy does. Temperature does not depend on amount of substance; energy does.

Boltzmann Distribution  source source

Law of Conservation of Energy  Energy is neither created nor destroyed in an 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. So chemists are interested in energy changes.  Thermochemistry!

Energy Transfer  Measure changes in heat. That is, the amount of energy transferred from one substance to another.  You can measure the energy lost somewhere or the energy gained somewhere else.  Cannot measure the absolute heat content of a system.

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

Perspective  When we talk about energy changes, we need a convention because direction is important.  Labels are from the system’s perspective!

Exothermic Change  System releases heat to environment What happens to the temperature of the 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? What happens to temperature of system?

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

Exothermic Change  System has a net loss in energy!  Environment has a net gain in energy!  Energy lost = Energy gained Canheat.mov Fe + S Fe + S

Endothermic Change  System absorbs heat from environment What happens to temperature of environment? What happens to temperature of environment?  Endo - Energy enters system (entrance)  What happens to the energy level of the system? What happens to temperature of system? What happens to temperature of system?

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

Endothermic Change  System has a net gain in energy!  Environment has a net loss in energy!  Energy lost = Energy gained. Endo1.mov

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. Leg cools down; cold pack warms up.

Quantity of heat transferred  Quantity 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 a single phase. To calculate heat gained or lost, use: 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 of heat energy required to raise the temperature of 1 gram of a substance by 1 o C.  Symbol = C  Specific heat = a physical constant. Different for each pure substance.

Specific heat capacity of selected substances.  Heat Capacities Heat Capacities Heat Capacities

source Calorimeter

source Another calorimeter source Tiger Graphics Tiger Graphics

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 we put in the water.

Calorimetry  Energy lost = Energy gained.  Difficult to monitor the “system.”  Easy to monitor the “environment” – that’s the water!  Energy lost/gained by environment = Energy gained/lost by system.

Calorimetry  10 grams of NaOH are 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 H 2 O Close together. Not interacting with H 2 O. Pulled apart & interacting with H 2 O.

Calorimetry Calculate the energy released by the NaOH in the previous problem as it dissolved in the water. Energy lost by NaOH = Energy gained by water. Easier to calculate from H 2 O perspective. Calculate the energy released by the NaOH in the previous problem as it dissolved in the water. Energy lost by NaOH = Energy gained by water. Easier 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  The temperature of the water increased from 22  C to 30  C.  30  C -22  C = 8  C =  T H2O.  What mass? Well, the temperature change was for the water, so you want the mass of the water. m H2O = 100 g.  Same goes for specific heat capacity. We’re going to calculate the heat absorbed by the water. C H20 = 4.18J/g 

Q = mC  T QQQQ = 100 g X 4.18 J/g X 8C QQQQ = 3344 Joules.

Stability and Energy  If energy is high, stability is low.  If energy is low, stability is high. Rubberband Rubberband Spring Spring Popper Popper Magnets Magnets Electrical Charges Electrical Charges

Atoms contain charged particles  Like charges Repel  Unlike charges Attract  The closer the charges, the greater the force.  If charges are far apart, charges don’t feel one another. (Think magnets!) Force goes to zero.

Electric Charges  Any 2 charges exert a force on each other.  Size of force depends on Distance between charges Distance between charges Signs of charges, positive or negative Signs of charges, positive or negative Size (magnitude) of charge Size (magnitude) of charge

Electric Charges vs. Pushing/Shoving  Pushing & shoving – direct contact  Electric charges – can exert a force over a distance. They don’t have to be touching.

Matter  Overall – electrically neutral  Composed of charged particles Electrons Electrons Protons Protons