Kinetics and Equilibrium

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Kinetics and Equilibrium

• Chapter 18

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Collision Theory

• a reaction is more likely to occur if reactant
  particles collide with proper energy and
  orientation
• Reaction Rate
• How fast the reaction proceeds

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Collision Theory

• Activation Energy (EA)
• Minimum energy that colliding particles must have
  in order to react

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Factors Affecting Reaction Rates

• Temperature
• Increasing temperature increases the reaction
  rate
• Concentration
• increasing the number of particles in a given
  volume (concentration) increases the reaction
  rate

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Factors Affecting Reaction Rates

• Surface Area
• increasing surface area increases reaction rate
• Catalyst
• the presence of a catalyst will often increase
  reaction rate
• Catalysts are not used up during a reaction

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Equilibrium

• Reversible Reaction
• Reaction in which conversion of reactants to
  products and conversion of products to reactants
  occurs simultaneously

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Equilibrium

• Chemical Equilibrium
• Rate of forward reaction is equal to rate of
  reverse reaction
• At Chemical Equilibrium, there is no net change
  in the actual amounts of the reactants and
  products.
• Amounts remain constant

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Equilibrium

• Saturated Solution
• Solid in equilibrium with dissolved particles

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LeChateliers Principle

• If a stress is applied to a system in dynamic
  equilibrium, the system changes in a way that
  relieves the stress

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Stresses Against Dynamic Equilibrium

• Change in concentration of reactant or product
• Change in temperature
• Change in pressure
• Only applies to reactions in the gas phase with
  unequal number of moles of gas.

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Example

• How does adding more carbon dioxide shift
  equilibrium?
• Equilibrium will shift towards reactants

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Example

• How will increasing the temperature affect
  equilibrium?
• Equilibrium will shift towards the reactants

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Example

• How will increasing pressure affect equilibrium?
• Equilibrium will shift towards the products
• Increasing pressure always shifts equilibrium
  towards the side with the least number of moles
  of gas.

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Common Ion Effect

• How will adding potassium chloride affect
  equilibrium?
• Equilibrium will shift towards the reactants

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Review

• Endothermic
• Energy being added
• N2 O2 182.6kJ ? 2NO
• Exothermic
• Energy being released
• 2CO O2 ? 2CO2 566kJ

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Potential Energy

• Potential Energy
• Energy stored in chemical bonds
• Heat of Reaction (?H)
• Energy absorbed or released during a chemical
  reaction
• PEProducts PEReactants

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Potential Energy Diagram

• Graphically shows energy released or absorbed
  during a reaction

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Exothermic Reaction
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Endothermic Reaction
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Table I

• Shows reactions with ?H
• ?H PEProducts PEReactants
• Endothermic
• ?H ()
• Exothermic
• ?H (-)

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Affect of a Catalyst

• Provides an alternate pathway for the reaction to
  proceed
• Decreases activation energy
• Increases reaction rate

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Affect of a Catalyst
Without Catalyst
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Entropy

• Measure of randomness or disorder
• Systems in nature tend to undergo changes towards
  lower energy and higher entropy
• The universe is lazy and disorganized

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Entropy

• Increasing Entropy
• Solid ? Liquid ? Gas
• Solid ? Dissolved