COMPETENCY GOALS 4

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COMPETENCY GOALS 4

• JACK BRITT HIGH SCHOOL

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What is light?

• Properties of light?
• Particles and Waves
• Light waves electromagnetic waves
• Electromagnetic radiation
• Wave Characteristics
• Amplitude
• Wavelength
• Frequency
• Speed

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Electromagnetic Radiation

• Increases in penetration, frequency, energy
• Decreases in wavelength

ROYGBIV
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The Bohr Model
Know how to find wavelength in nanometers and
match it with the color of light emitted.
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Amplitude

• The height of the wave measured from the origin
  to its crest or peak.
• Determines the brightness or intensity of the
  light.
• A measure of the maximum rise or fall of a wave.

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Wavelength

• The distance between successive crests of the
  wave.
• Includes one crest and one trough.
• Contains three consecutive nodes (crest to crest
  or trough to trough).
• ? meters.

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Frequency

• Tells how fast a wave oscillates up and down.
• Measured by the number of times a light wave
  completes a cycle of upward and downward motion
  in one second.
• Repetitions or cycles per second.
• ? 1/s hertz Hz.

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Velocity

• Light regardless of its wavelength moves at a
  constant speed.
• Speed of light (c) 3.00 x 108 m/s.
• Wavelength vs. Frequency
• c ? x ?
• or
• ? c / ?

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Exothermic and Endothermic Reactions

• Heat
• Joule The SI unit for energy and heat.
• Bond breaking requires energy
• vs.
• Bond forming which releases energy!

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Exothermic

• Exothermic reactions release heat.
• Heat is a product.
• Combustion reactions.

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Endothermic

• Endothermic reactions absorb heat.
• Heat is a reactant.

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Enthalpy (?H)

• The enthalpy of a substance is its energy plus a
  small-added term that includes the pressure and
  temperature of the substance.
• When the pressure remains constant, the heat
  absorbed or released during a chemical reaction
  is equal to the enthalpy change for the reaction.
• Heat transfer and the sign of the enthalpy
  change
• Positive Endothermic Heat absorbed
• Negative Exothermic Heat released

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Enthalpy of Reactions ?Hrxn Hproducts -
Hreactants

• The enthalpy change for a reaction is equal to
  the heat absorbed or gained during the reaction.
• Enthalpy change is the enthalpy of the products
  minus the enthalpy of the reactants.
• The amount of heat absorbed / released is
  dependent on the quantity (mole).

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Enthalpy and the Spontaneous Process

• Review enthalpy diagrams.
• Spontaneous Process a process that proceeds on
  its own, without any outside intervention.
• Spontaneous vs. Non-Spontaneous
• Exothermic Endothermic
• No catalyst Catalyst
• Energy of Activation The difference between the
  energy of an activated complex and the energy of
  the reactants of a chemical reaction.

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Entropy (?S)

• Order vs. Disorder.
• Relate the states of matter and the degree of
  order.
• Entropy A quantitative measure of the disorder,
  or randomness, in the substances involved in a
  reaction.

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Entropy Changes?Srxn Sproducts - Sreactants

• Entropy Increases
• Sproducts gt Sreactants
• Entropy Decreases
• Sproducts lt Sreactants
• Predicting entropy increases
• Gases are formed from liquids or solids.
• Solutions are formed from liquids and solids.
• There are more molecules of gas as products than
  there are as reactants.
• The temperature of a substance is increased.

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Entropy Criterion

• In any spontaneous process, the overall entropy
  of the universe always increases.
• Entropy of the Universe
• ?Suniverse ?Sreaction ?Ssurroundings
• A reaction is spontaneous when ?Suniverse is
  positive.
• Change in entropy of the reaction (see
  predicting).
• Change in entropy of surroundings (endo vs. exo)
• If ?H is (-), then ?Ssurroundings is ().
• If ?H is (), then ?Ssurroundings is (-).

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SUMMARY
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Entropy and Gibbs Free Energy (G)

• Spontaneity depends on entropy and enthalpy.
• Gibbs proposed a thermodynamic concept to
  simultaneously incorporate the concepts of
  entropy and enthalpy.
• ?G ?H - T?S

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Free Energy Spontaneity

• If ?G is negative, the reaction is spontaneous
  and can proceed on its own.
• If ?G is positive, the reaction is not
  spontaneous and requires a sustained input of
  energy to make it occur.
• If ?G is zero, the reaction is at equilibrium.

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?G Spontaneity
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Free Energy and Work

• Spontaneous reactions release free energy that
  can perform work.
• ?G represents the maximum work that a spontaneous
  process can perform.
• ?G for a nonspontaneous reaction is the minimum
  amount of work that must be performed to make a
  reaction occur.

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Hesss Law

• If a series of reactions are added together, the
  enthalpy change for the net reaction will be the
  sum of the enthalpy changes for the individual
  steps.
• ?Hnet ?H1 ?H2
• Two Rules
• If the coefficients of an equation are multiplied
  by a factor, the enthalpy change for the reaction
  is multiplied by the same factor.
• If an equation is reversed, the sign of ?H
  changes also.

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Calorimetry

• The study of heat flow and heat measurement.
• How do you measure an enthalpy change of a
  reaction?
• Calorimetry experiments determine the enthalpy
  changes of reactions by making accurate
  measurements of temperature changes produced in a
  calorimeter.

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Heat and Temperature

• Exothermic reactions release heat to
  surroundings. The size of the temperature
  increase depends on the amount of heat released
  and the heat capacity of the surroundings.
• Heat capacity The amount of heat needed to
  raise the temperature of the object 1oC.
• Heat capacity depends on the objects mass and its
  composition.
• Specific heat (C) The heat capacity of 1 gram
  of a substance.
• C of H2O 4.184 J/g-oC.

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Half-life

• The half-life of a radioactive isotope is the
  time it takes for one half of a sample of that
  isotope to decay.
• Uranium-238 4.5 billion years (alpha decay).
• Carbon-14 5,730 years (beta decay).
• Sample problems.
• HW Worksheet 24-1
• Set up notebooks for lab 4.

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RadioactivityAlpha, Beta, and Gamma

• Distinguished by charge, mass, and penetrating
  power.
• Radioactive decay when an atom emits one of
  these kinds of radiation.
• Decay nucleus decays to form a new nucleus
  releasing radiation in the process.
• Nuclear reactions change the composition of the
  atoms nucleus.

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Nuclear Equations

• Keep track of the reactions components.
• The sum of the mass numbers and atomic numbers
  are the same before and after.
• Decay (emission) there is only one thing on the
  left of the ?
• Bombardment there are two things
• on the left

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Effects of Radiation

• Harmful to living things
• Effects depend on the amount and type.
• Effects on living tissue
• Ionizing radiation disrupts living cells.
• Somatic damage direct.
• Genetic damage reproduction.

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Uses of Nuclear Chemistry

• Radioactive dating.
• Smoke detectors.
• Imaging.
• Radiotracers.
• Cancer therapy.
• Food preservation.
• Energy.

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Measuring Radiation

• Equipment
• Dosimeter.
• Geiger counter.

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Nuclear EnergyNuclear Fission

• A large nucleus is split into two smaller nuclei
  of approximately the same mass.
• The missing mass energy.
• Nuclear chain reactions.
• Nuclear reactors.
• Three Mile Island (loss of coolant).
• Chernobyl (failure of the moderator).
• Waste disposal (fuel rods and burial).

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Nuclear EnergyNuclear Fusion

• Two small nuclei join to form a large nucleus.
• Difficult to produce and control.
• Electron cloud repulsion.
• Nucleus repulsion.
• Benefits
• Uses hydrogen abundant.
• No radioactive waste.
• Problem
• High temps required.

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Half-life

• The half-life of a radioactive isotope is the
  time it takes for one half of a sample of that
  isotope to decay.
• Uranium-238 4.5 billion years (alpha decay).
• Carbon-14 5,730 years (beta decay).
• Sample problems.
• HW Worksheet 24-1
• Set up notebooks for lab 4.