Chemical

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Chemical Kinetics
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GOALS
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1. Explain the role of activation energy and
degree of randomness in chemical reactions
3. Investigate the effects of a catalyst on
chemical reactions and apply it to everyday
examples.
4. Experimentally determine indicators of a
chemical reaction specifically precipitation, gas
evolution, water production, and changes in
energy to the system.
5. Demonstrate the effects of changing
concentration, temperature, and pressure on
chemical reactions.
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Chemical Reactions and Energy
GOAL Explain the role of activation energy and
degree of randomness in chemical reactions
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Reaction Directions

• Physical and Chemical systems attain the lowest
  possible energy.
• Law of disorder the natural tendency is for
  systems to move in the direction of maximum
  disorder (or randomness)- 2nd law of
  thermodynamics
• Entropy is a measure of the disorder of a system.
• An increase in entropy favors spontaneous
  chemical reactions decrease favors the
  nonspontaneous reaction.

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• Rxns are favorable when they result in a decrease
  in energy and an increase in entropy (disorder)
• Rxn can proceed if products have more order IF
  energy is supplied.

Entropy is a measure of the disorder of a system.
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• 2nd Law of thermodynamics
• The total Entropy of the universe is constantly
  increasing. The state of maximum entroy is the
  most stable state.

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Chemical Reactions and Energy
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• All chemical reactions release or absorb energy.
• Heat, light, sound
• Chemical reactions are the making and breaking or
  bonds.

Enthalpy (?H) Heat Energy of the System
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1. Exergonic
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• Chemical reactions that releases energy are
  called exergonic.
• Glow sticks
• If heat is released, it is called exothermic
• Combustion
• Decease in Enthalpy (?H) of the system

Ch 17
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2. Endergonic

• Chemical reactions that require energy are called
  endergonic.
• Ex Cold Packs
• If heat is absorbed, it is called endothermic
• Increase in Enthalpy (?H) of the system

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Ch 17
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Rates of Chemical Reactions
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Intro Clip
Chemical Kinetics The area of chemistry that
concerns reaction rates.
St. Dev Chemical reactions- Kinetics Clip
Goals Investigate the effects of a catalyst on
chemical reactions and apply it to everyday
examples. Demonstrate the effects of changing
concentration, temperature, and pressure on
chemical reactions.
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Rates of Chemical Reactions
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Collision theory

• For a chemical reaction to occur,
  the reactant particles must collide. But
  collisions with too little energy do not produce
  a reaction.
• - The particles must have enough energy for the
  collision to be successful in producing a
  reaction.
• - The rate of reaction depends on the rate of
  successful collisions between reactant particles.
  
• The more successful collisions there are, the
  faster the rate of reaction

Collision Theory (Youtube) Clip
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Measuring the Rates of Chemical Reactions

• Rate Expressed as the amount of reactant
  changing per unit of time.
• What are some ways that you might be able to
  measure the rate of a reaction?
• Amount of a product produced over time
• Amount of reactant used up over time.

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Factors Affecting Reaction Rates

1. Temperature
2. Concentration
3. Particle Size (surface area)
4. Pressure
5. Catalysts (the match maker)

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1-Temperature

• Particles can only react when they collide. If
  you heat a substance, the particles move faster
  and so collide more frequently. That will speed
  up the rate of reaction.

• increase the temp, more molecules are able to
  move faster, so more of them will have the
  minimum energy for the reaction to take place.

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2- Concentration

• Increasing the concentration, increases the
  probability of a collision between reactant
  particles because there are more of them in the
  same volume and so increases the chance of a
  successful collision forming products.

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3-Particle Size
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Smaller in size means larger in surface area and
hence a faster rate of reaction.
No so fun fact On Feb. 7, 2008 a huge explosion
and fire occurred at the Imperial Sugar Refinery
in Georgia, USA causing 14 deaths and seriously
injuring 38 others. The explosion was caused by
accumulated sugar dust in the packaging facility
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4-Pressure
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• Increasing the pressure on a reaction involving
  reacting gases increases the rate of reaction.
• Changing the pressure on a reaction which
  involves only solids or liquids has no effect on
  the rate.

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5-Catalysts

• A catalyst is a substance which speeds up a
  reaction, but is chemically unchanged at the end
  of the reaction.

• Increases the frequency of collisions
• Changes orientation of molecules
• Can reduce intramolecular forces within reactants

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Activation Energy

• To understand what catalysts do, we need to go
  back and talk about reactions and energy..
• Collisions only result in a reaction if the
  particles collide with enough energy to get the
  reaction started.
• This minimum energy required is called the
  activation energy for the reaction.

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Activation Energy

• The minimum energy that colliding particles must
  have in order to react is called activation
  energy.
• energy can be used to stretch, bend, and
  ultimately break bonds, leading to chemical
  reactions

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Catalysts
A catalyst provides an alternative route for the
reaction by lowering its activation energy so
more particles will have enough energy to react.
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Catalysts
Biological Catalyst Enzymes Inorganic
catalyst Metals

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• Catalysts are not used up in the reaction.

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Catalysts and Inhibitors

• Some reactions proceed too fast.
• They can be slowed down by inhibitors.
• EX Preservatives in food

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Everyday examples of Rates of Reactions

1. Enzymes

2. Catalytic converters Catalytic converters
change poisonous molecules like carbon monoxide
and various nitrogen oxides in car exhausts into
more harmless molecules like carbon dioxide and
nitrogen. They use expensive metals like
platinum, palladium and rhodium as the
heterogeneous catalyst. The metals are deposited
as thin layers onto a ceramic honeycomb. This
maximises the surface area and keeps the amount
of metal used to a minimum. Taking the reaction
between carbon monoxide and nitrogen monoxide as
typical
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Reversibility of Reactions

• Some reactions are reversible
• Chemical Equilibrium
• When the rates of the forward rxn and the reverse
  rxn are equal
• Dynamic state
• Rxn still continues to happen

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• Funny Review Clip

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