Updated August 2006

Created by C. IppolitoAugust 2006

Energy

Objectives:1. identify various forms of energy2. describe energy changes during a chemical reaction3. distinguish between heat energy and temperature4. solve calorimetry problems5. describe interactions between electrostatic charges

Created by C. IppolitoAugust 2006Updated August 2006

Concept of Energy•EnergyEnergy

–ability to do work–can be changed into work under proper conditions–can be converted from one form into another–can be transmitted from one particle to another

•WorkWork–done when an object, in response to a force (push or pull), moves some distance–work = force x distance

Created by C. IppolitoAugust 2006Updated August 2006

Mechanical Energy• energy possessed by macroscopic

(large) particles– Potential EnergyPotential Energy (EP)

• depends on the position of the object in respect to other objects

• stored energy

– Kinetic EnergyKinetic Energy (EK)• depends upon the motion of an object in

respect to other objects• “working” energy

Created by C. IppolitoAugust 2006Updated August 2006

Nonmechanical Energy• energy associated with submicroscopic

(small) particles– chemical energy– electrical energy– electromagnetic energy a.k.a. radiant energy– sound energy– magnetic energy– heat energy

• joule (J) is the SI unit that measures energy – named to honor James Joule, British scientist

to study all forms of energy

Created by C. IppolitoAugust 2006Updated August 2006

Matter and Energy• Law of the Conservation of MatterLaw of the Conservation of Matter

– Matter is always conserved. This means the amount of matter is constant, it is neither created nor destroyed. It can only change form.

• Law of the Conservation of EnergyLaw of the Conservation of Energy– Energy is always conserved. The amount of

energy in the universe is also constant, it is neither created nor destroyed. It too can only change form.

• Albert Einstein– Matter can be changed into energy and

energy can be changed into matter with his now famous equation

• E = mc2

– Law of the Conservation of Mass-Law of the Conservation of Mass-EnergyEnergy

• Mass-Energy is always conserved. The amount of Mass-Energy in the universe is also constant, it is neither created nor destroyed. It too can only change form.

Created by C. IppolitoAugust 2006Updated August 2006

Energy and Chemical Change• All chemical changes are

accompanied by a change in energy– Endothermic ReactionEndothermic Reaction

• Heat energy is absorbed• Products have more energy than reactants• Surroundings become colder

– Exothermic ReactionExothermic Reaction• Heat energy is released• Products have less energy than reactants• Surroundings become warmer

• Activation EnergyActivation Energy– Minimum amount of energy needed to

start any chemical reaction

Created by C. IppolitoAugust 2006Updated August 2006

Heat Energy and Temperature• Temperature based on

“hotness” and “coldness”– Celsius ScaleCelsius Scale

• Anders Celsius• 0oC water freezes 100oC water

boils

– Kelvin scaleKelvin scale• William Kelvin• Based on theoretically lowest

temperature of absolute zero where all molecular motion stops

Created by C. IppolitoAugust 2006Updated August 2006

Temperature Conversions• To convert Celsius to Kelvin

– Add 273 to Celsius temperature• 50oC = ? K• 50oC + 273 = 323 K

• To convert Kelvin to Celsius– Subtract 273 from Kelvin temperature

• 30 K = ?oC• 30 K – 273 = -243 oC

Created by C. IppolitoAugust 2006Updated August 2006

Heat Measurement•Calorimeter

–Apparatus used to measure heat by rise or fall of temperature of water

•Specific Heat Capacity (CP)

–amount of joules needed to raise 1g of a substance 1oC–measured as –listed in “Handbook of Chemistry and Physics”

•CP water = 4.18 J/goC

•CP aluminum = 0.903 J/goC

jou lesgram s C( ) (d eg )

Created by C. IppolitoAugust 2006Updated August 2006

Heat Calculations•Equation:

–Heat transferred = mTCP water

•M = mass of waterT = change in water temperature•CPwater = 4.18 J/goC

•How much energy is needed to raise 40 g of water from 20.0oC to 36oC?

Known: CPwater = 4.18 J/goC

Tinitial = 20oC

Tfinal = 36oC

m = 40 g

Unknown: Heat transferred

hea tJ

g Cg C C

hea tJ

g Cg C

hea t J

hea t J J

oo o

oo

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4 1 84 0 3 6 2 0

4 1 84 0 1 6

4 1 8 4 0 1 6

2 6 7 5 2 6 8 0

Created by C. IppolitoAugust 2006Updated August 2006

Heat Calculations (con’t)•How much heat energy is lost when a solid ingot of aluminum with a mass of 4 110 g cools from 660oC to 25.0oC?Known: CPaluminum = 0.903 J/goC

Tinitial = 660oC

Tfinal = 25.0oC

m = 4 110 g

Unknown: Heat transferred

hea tJ

g Cg C C

hea tJ

g Cg C

hea t J

hea t J J

oo o

oo

(.

) ( ) ( . )

(.

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( . ) ( ) ( )

.

0 9 0 34 11 0 6 6 0 2 5 0

0 9 0 34 11 0 6 3 5

0 9 0 3 4 11 0 6 3 5

2 3 4 8 8 6 5 2 3 1 0 6