Matter and Energy Chapter 2

1
Matter and Energy Chapter 2

• 2.1 Energy

2
Objective/Warm-Up

• Students will be able to apply their knowledge of
  density to a real world problem.
• How can you use density to determine if something
  will sink or float in water?

3
Energy Changes

• Energy the capacity to do work
• All physical and chemical changes involve changes
  in E.
• Endothermic describes a process in which heat
  is absorbed from the environment

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Energy Changes

• Exothermic describes a process in which a
  system releases heat into the environment
• NaOH H2O
• Evaporation the change of a substance from a
  liquid to a gas

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Law of Conservation of Energy

• Law of Conservation of Energy in a chem. or
  phys. change, E is neither created nor destroyed
• It can be transferred or converted
• Chemical, mechanical, light, sound, heat,
  electrical

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Energy

• Kinetic Energy the E a moving object has b/c of
  its motion
• Potential Energy the E an object has b/c of its
  position

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E Transfer

• In chemistry, the most common E transfer is in
  the form of heat
• Heat the energy transferred b/t objects that
  are at different temps.
• Temperature a measure of the average kinetic E
  of the particles in a sample of matter.

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Temperature Scales
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Equations for Temp Conversions

• t (C) T(K) 273.15 K
• T(K) t (C) 273.15 C
• Convert 25 C to Kelvin
• T(K) 25 273.15 C 298.15 K
• Convert 1500 K to C
• t (C) 1500 273.15 K
• t (C) 1226.85 C

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Specific Heat Capacity

• Specific Heat Capacity the amount of E required
  to raise the temp of 1 gram of a substance by 1
  Kelvin under constant T P
• Different for each element
• Measured in J/gK joule is the SI unit for E
• Determined experimentally

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Objective/Warm-Up

• Students will be able to calculate change in
  temperature and specific heat capacity.
• What do the terms endothermic and exothermic
  mean?
• How would you know that a reaction is endothermic
  or exothermic?

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Calculations-Specific Heat

• Q m c ?T
• Q heat energy (J)
• m mass (g)
• c specific heat (J/gK or J/goC)
• ?T change in temperature (T final T
  initial) (K or oC)

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Calculations

• Calculate the heat required to increase the
  temperature of 15 g of aluminum by 10. K. The
  specific heat of aluminum is 0.897 J/gK
• Q 15g x 0.897J/gK x 10.K
• Q 134.55 J
• 130 J with sig figs

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Calculations

• How much energy is given off when 25 grams of
  lead cools by 25 K if the specific heat of lead
  is 0.129 J/gK?
• Q 80.625 J
• 81 J with sig figs

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Objective/Warm-Up

• Students will be able to convert temperatures and
  calculate heat capacity.
• Warm-Up Concept Review worksheet

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Mass and Energy

• Thought to be unrelated
• Emc2 relates mass and energy
• c is equal to the speed of light of 2.998 x 108
  m/s
• In a nuclear power plant, mass is converted to
  energy

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E mc2

• How much E is obtained from a 1.00 gram object?
• E mc2
• E 1.00 g x (2.998 x 108 m/s)2
• E 8.988 gm2/s2 or 8.988 x 1013 J
• Its enough to raise a burger to your mouth 90
  trillion times

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Assignment

• Do the section review on page 45. Do numbers
  1-13.