Reaction Kinetics and Equilibrium

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Reaction Kinetics and Equilibrium

• How compounds react with each other

2
Collision Theory

• A reaction is most likely to occur if reactant
  particles collide with the proper energy and
  orientation
• http//www.chem.iastate.edu/group/Greenbowe/secti
  ons/projectfolder/animations/NOO3singlerxn.html

3
Reaction Rate Affecting Factors

• Nature of Reactants
• Concentration
• Surface Area
• Temperature
• Presence of a Catalyst
• Pressure for Gases

4
Nature of Reactants

• Factors that contribute to reaction rate
• - Electronegativity
• - Ionization energy
• - Atomic Radius.

5
Bonding on Rate of Reaction

• Covalent bonds require more energy during
  collisions due to a greater number of bonds
  needed to be broken and reformed.
• Ionic Bonds are faster to react and require less
  energy during a collision.

6
Concentration

• We measure concentration by the number of moles
  there are in a L of solution (Molarity).
• More moles more collisions
• Ex Burning paper. When the oxygen
  concentration is low the paper burns slowly.
  Raise the amount of oxygen the paper burns
  faster.
• http//www.coolschool.ca/lor/CH12/unit1/U01L01.htm
  

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Surface Area

• The larger the surface area the easier it is to
  react because there are more chances for
  collision.

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Temperature

• The average kinetic energy of molecules in a
  compound.
• The more molecules move the higher the
  temperature.
• Higher temperature results in more collisions

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Presence of a Catalyst

• A substance whose presence increases the rate of
  a chemical reaction.
• Catalysts change (decrease) the activation
  energy which increases the rate of reaction

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Activation Energy

• Activation energy is the minimum energy required
  to initiate a reaction.
• When particles collide with the right amount of
  activation energy it breaks the existing bond.

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Energy

• Kinetic Energy (motion) this the energy of work
  being done
• Potential Energy (static) the potential for
  something to do work
• Remember that there are many types of energy
• - electrical
• - thermal
• - mechanical
• - electromagnetic
• - nuclear

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Endothermic vs. Exothermic Reactions

• Exothermic (exit) reactions give off heat energy
  during a chemical reaction
• Endothermic (enter) reactions absorb heat energy
  during a chemical reaction
• http//schools.matter.org.uk/Content/Reactions/Bo
  ndActivation.html

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Potential Energy Diagram

• Used to show the energy released or stored in
  endothermic and exothermic reactions
• http//www.saskschools.ca/curr_content/chem30/mod
  ules/module4/lesson4/potentialenergydiagram.htm

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Reading Energy Diagrams

• THE Y AXIS Potential energy of the reaction
• THE X AXIS Reaction as it takes place over time
  
• CURVE Represents the potential energy at each
  step of a chemical reaction

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Reading Energy Diagrams

• EXOTHERMIC REACTION energy given off during a
  reaction
• LOOK AT THE CURVE AND SEE IF IT ENDS AT A LOWER
  VALUE
• The energy of the products is lower than the
  energy of the reactants

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Reading Energy Diagrams

• ENDOTHERMIC energy is absorbed during a
  reaction
• The energy of the products is higher than the
  heat of the reactants
• LOOK AT THE CURVE AND SEE IF IT ENDS AT A HIGHER
  VALUE
• ACTIVATION ENERGY The amount of energy needed
  to reach the peak of the curve
• SUBSTRACT THE ENERGY AT THE PEAK OF THE CURVE
  FROM THE INITIAL ENERGY

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Effect of a Catalyst of Activation Energy
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Catalysts Continued

• A catalyst lowers the activation energy required
  for the reaction to occur. By lowering the
  activation energy, the chemical reaction can
  occur much more quickly.

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Reversible Reactions

• Not all reactions go completely to completion
  (all reactants are used up)
• Instead, some reactions can occur both forward
  and reverse at the same time. A reversible
  reaction is symbolized by double arrows
• 2SO2(g) O2(g) 2SO3(g)

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Equilibrium

• The rate at which the products are formed is at
  the same rate that the reactants are formed.
• Equilibrium is represented with a double
  arrow. Example

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Equilibrium
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Entropy

• The measure of the randomness or disorder of a
  systems energy.
• The greater the randomness the greater the
  entropy.

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Entropy of Substances

• As a substance goes from solid to liquid to gas,
  entropy increases.
• Systems in nature tend to undergo changes toward
  low energy and high entropy (they want to lose
  energy and gain freedom)

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Change of State (review)

• A change of state, also called a phase change, is
  the conversion of a substance from one of the 3
  states of matter to another. A change of state
  always involves a change in energy.

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Heating and Cooling Curves
Animation

• Shows how a substance changes states at each
  temperature increase over time.

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Phase Diagram
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Equilibrium Review

• Some chemical reactions are reversible
• When a reaction is occurring both forward and
  reverse at the same rate, equilibrium is reached
• Example
• N2 3 H2 2 NH3 energy

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Le Chatliers Principle
Video

• When a system at equilibrium is subjected to a
  stress (a change in concentration, temperature,
  or pressure), the equilibrium will shift in the
  direction that tends to counteract the effect of
  the stress.

29
Le Chatliers Principle

• Example
• N2 3 H2 2 NH3 energy
• If the concentration of Nitrogen is increased,
  the reaction will shift to the right and favor
  the products side, making more ammonia and giving
  off more heat.

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Le Chatlier

• Example
• N2 3 H2 2 NH3 energy
• If the temperature is increased, the reaction
  will shift to the left and favor the reactants
  side, making more N and H

31
Effect of Pressure on Equilibrium

• Example
• N2 3 H2 2 NH3 energy
• (4 moles gas) (2 moles gas)
• If the pressure is increased, the reaction will
  shift to the right, favoring the side with the
  lower number of moles of gas

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Heat and Temperature

• Heat (J or calories) a transfer of energy from
  a body of higher temperature to a body of lower
  temperature. Thermal energy is associated with
  the random motion of atoms and molecules.
• Ex) steam v water
• Temperature a measure of the average kinetic
  energy of the particles of a substance.
  Temperature is not a form of energy.
• Question What state of matter has the most
  energy? GAS

33
Heat Calculations

• Specific Heat Capacity the amount of energy
  required to raise the temperature of a substance
  one degree.
• Ex Takes more energy to heat a swimming pool
  than a cup of water
• Specific heat Capacity of H2O (l) 4.18 J/g X C

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Calculations con

• Fusion melting
• Heat of Fusion the amount of heat needed to
  convert unit mass of a substance from a solid to
  a liquid at constant temperature.
• - when ice is melting the kinetic energy stays
  the same
• Heat of Fusion of H2O 334 J/g

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Calculations con

• Heat of Vaporization the amount of heat needed
  to convert a unit mass of a substance from a
  liquid to a gas at constant temperature.
• - when ice is boiling the kinetic energy stays
  the same
• Heat of V of H2O 2260 J/g
• TABLE B in Reference Table

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Calculations con.

• Q mC?T
• Q mHf
• Q mHv

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Vapor Pressure

• In every liquid, some particles are far enough
  away from each other to be considered gas but are
  pushed down by atmospheric pressure. When in
  liquid, some particles are far enough apart to
  escape their neighboring molecules and enter the
  gas phase (vapor). As temperature increases,
  particles gain more energy and more particles
  escape from the surface. The pressure these
  gaseous particles exert is called vapor pressure.
  As temp increases, vapor pressure increases.

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Vapor Pressure con.

• Vapor pressure eventually builds up enough to
  equal atmospheric pressure. When it surpasses
  atmospheric pressure, the liquid boils and allows
  the gaseous particles to escape.
• Vapor Pressure pressure gaseous particles exert
  upward