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Chemistry Review
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image Chapter 17: Equilibrium - concept summary image
image image Reaction Rates and Equilibrium Section 17.1
¨ Collision model for chemical reactions
• Reactants must collide to react.
• A certain threshold energy (the activation energy, Ea) must be supplied by the collision for a reaction to occur.
¨ A catalyst
• Speeds up a reaction without being consumed.
• Provides a new pathway for the reaction that has a smaller Ea.
• Enzymes are biological catalysts.
¨ Chemical equilibrium is established when a chemical reaction is carried out in a closed vessel.
• The concentrations of both reactants and products remain constant over time.
• Equilibrium is a highly dynamic state on the microscopic level.
· Forward rate = reverse rate
• In homogeneous reactions, all reactants and products are in the same phase.
• In heterogeneous reactions, one or more reactants or products are in different phases.
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image Characteristics of Equilibrium Section 17.2
¨ The equilibrium expression is based on the law of chemical equilibrium.
• For the reaction
  aA + bB Û cC + dD
 
• The equilibrium constant (K) is constant for a given chemical system at a given temperature.
• The equilibrium position is a set of equilibrium concentrations that satisfy K.
• There are an infinite number of equilibrium positions.
¨ Heterogeneous equilibria contain reactants or products in different phases.
• A pure liquid or solid never appears in the equilibrium expression.
image Application of Equilibria Section 17.3
¨ Le Châtelier’s principle states that when a change is imposed on a system at equilibrium the position of the equilibrium shifts in the direction, which reduces the effect of that change.
¨ Applications of equilibria
• The value of K for a system can be calculated from a known set of equilibrium concentrations.
• Unknown equilibrium concentrations can be calculated if the value of K and the remaining equilibrium concentrations are known.
• The equilibrium conditions also apply to a saturated solution containing less excess solid, MX(s).
· Ksp = [M+][X–] = Solubility product constant.
· The value of the Ksp can be calculated from the measured solubility of MX(s).
image Terms introduced (do you know them ?):
Activation Energy (Ea)
Chemical Equilibrium
Collision Model
Enzyme
Equilibrium		 Equilibrium Constant
Equilibrium Expression
Equilibrium Position
Heterogeneous Equilibrium
Heterogeneous Reaction		 Homogeneous Equilibrium
Homogeneous Reaction
Law of Chemical Equilibrium
Le Châtelier’s Principle
Solubility Product Constant
  (Ksp)
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