Energy Flashcards (unit 3)

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Energy Flashcards(unit 3)
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ENERGY

• The ability to do work

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Potential Energy

• Energy of position.
• Stored energy.

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Kinetic Energy

• Energy of motion
• Depends on how heavy how fast

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Radiant Energy

• Electromagnetic Energy

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Units of Energy

• Joules SI system
• Calories - English

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Energy in Chemistry

• Chemical Potential Energy stored in chemical
  bonds
• Heat form of energy that flows between objects
  at different temperatures.
• Heat form of energy associated with the motion
  of atoms molecules. Hot atoms move fast!

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Direction of heat flow

• Hot to Cold

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Q

• Symbol for heat energy

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Temperature

• A measure of the avg. kinetic energy of the
  particles of a system.
• Temperature is NOT energy.

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As the temperature ?, the avg. kinetic energy

• Increases!

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As the temperature ?, the avg. kinetic energy

• Decreases!

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When the temperature is constant, the avg.
kinetic energy

• is constant!

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Law of Conservation of Energy

• Total energy is conserved.
• Energy before Energy after
• Energy lost Energy gained
• Energy can be converted from 1 form to another.

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Energy of Universe is conserved
Universe
Energy can move between the system and the
environment.
Environment
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EXO - energy leaves system (exits).
Temperature of environment ? Temperature of
system ?
System has a net loss in energy! ?H is ve.
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Exothermic Process

• System releases energy (heat) to environment.

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Endo - Energy enters system (entrance)
Temperature of environment ?. Temperature of
system ?.
System has a net gain in energy! ?H is ve.
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Endothermic Process

• System absorbs energy (heat) from environment

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Quantity of heat transferred depends on

1. Temperature change
2. Mass of substance
3. Specific Heat of substance

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Calculating Heat Transferred
Simple system Pure substance in a single phase.
To calculate heat gained or lost, use
Q mC?T
Q amount of heat transferred m mass of
substance C specific heat capacity of the
substance (Table B). ?T temperature change
Tfinal Tinitial
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Q mC?T

• Equation used to calculate energy change when a
  substance in 1 phase is heated or cooled.

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Calculating energy changes in H2O
Q
C
m
?T
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Dissolving

• When 10 g NaOH dissolves, the temperature of the
  H2O increases.

Add 100 g H2O
Styrofoam Cup
Close together. Not interacting with H2O.
Pulled apart interacting with H2O.
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Calorimetry

• The NaOH is the system.
• The H2O is the environment.

Styrofoam Cup
Initial temperature of water 22?C
Temperature 30?C
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Calculating energy changes in H2O
Q
CH2O 4.18J/g?
100g
8?
Q 3344 Joules
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Exothermic
In a calorimetry expt, H2O is the environment.
The system is the stuff in the water. If the
temperature of the H2O ?, the process was
______________.
exothermic
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Endothermic
In a calorimetry expt, H2O is the environment.
The system is the stuff in the water. If the
temperature of the H2O ?, the process was
______________.
endothermic
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Energy and Stability
If energy is high, stability is low. If enrgy is
low, stability is high.
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Energy Changes at Phase Changes
Gas
Going Up the ladder Endothermic Process Net
gain in energy.
Potential Energy of System
Liquid
Going Down the ladder Exothermic Process Net
loss in energy.
Solid
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What kind of intermolecular forces do solids have?
Strong IMF!
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What kind of intermolecular forces do gases have?
Weak IMF!
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What changes can we apply to cause a substance to
go from the gas phase to the solid phase?
Lower the temperature and increase the pressure.
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What changes can we apply to cause a substance to
go from the solid phase to the gas phase?
Raise the temperature and decrease the pressure.
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Name 2 substances that sublimate.
I2 and CO2 (dry ice)
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What kind of intermolecular forces do I2 and CO2
have?
Weak IMF. They sublimate easily.