Chemistry I
Chapter 15 – Chemical Equilibrium
Test review
TEST: Friday, April 30, 2010
Planned format:
 6 true/false; 2 points each
 19 multiple choice; 2 points each
 3 Short answer/problems
o LeChatlier’s Principle question
 Given an equation; predict which way the equilibrium will shift in response to different stresses
 Add or remove a reactant
 Add or remove a product
 Add or remove heat (increase or decrease the temperature)
 Increase of decrease the volume (decrease or increase the pressure)
 Add a catalyst
o Ksp problem
 Write the equation for the dissolving of a slightly soluble compound
 Write the Ksp expression
 Calculate the molar solubility (or g/L) given the Ksp value
 Calculate the Ksp given the concentrations (or information to determine the concentrations of the ions)
o ICE-box equilibrium problem
Bonus problem (ICE-box equilibrium problem with an “x” to solve for – See problem #15(b) on the first WA))
Topics for T/F - MC:
 Collision theory
o Collision has to occur
 What factors increase the number of collisions
 Increased concentration
 Increased temperatures (faster moving molecules – more collisions)
 Increase the surface area of the reactants
o Enough energy – activation energy (Ea)
 What factors increase energy of the reactants
 Increased temperature (faster moving molecules – more kinetic energy – more molecules have Ea)
o Correct orientation
 What factors affect orientation
 Not many, maybe a catalyst that holds one reactant in place…
 Activation energy – energy that must be overcome to get a reaction to form products (energy “hill”)
o lower activation energy – faster reactions
o is lowered with the addition of a catalyst
 Potential energy diagrams
o Where is the activation energy
o Where is the H, enthalpy of reaction
o Is it endothermic or exothermic?
o How does a catalyst change the diagram?
 Dynamic equilibrium
o When the rates of the forward and reverse reactions are equal
 NOT When the amounts of reactant and product are equal
 NOT When the reaction has come to a stop (it doesn’t stop)
 Given a balanced chemical equation, write the Keq expression
o And vice versa, given the Keq expression, determine the balanced equation
o Watch for solids and liquids in the equations – they are not included in the Keq expression.
o Be able to calculate the value for Keq given some concentrations (not necessarily all of the concentrations – some you
may have to figure out)
 What factor will change the value of the Keq? (Temperature only)
o Changes in concentration of the substances DO NOT CHANGE the value of K eq.
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The magnitude of Keq
o Keq much larger than one indicates a reaction favoring the products (equilibrium lies to the right)
o Keq much less than one indicates a reaction favoring the reactants (equilibrium lies to the left)
LeChatlier’s Principle – When a stress is applied to a system at equilibrium, the equilibrium may shift to relieve that stress
o You should be able to predict shifts in equilibrium (or increases/decreases in a reactant or product) given these
stresses:
 Changes in concentration (adding or removing a reactant or product)
 Changes in temperature (adding or removing energy//heat) (you need to know if it is endo or exothermic)
 Changes in volume (or pressure)
o What will not cause a shift in equilibrium position
 Addition of a catalyst – a catalyst increases the rate of reaction, does not change the position of equilibrium
 Changes in pressure or volume when the same number of moles of gas is present on both sides of the
reaction
 Addition or removal of a pure liquid or solid
 Addition of an inert gas (although it increase the total pressure, it does not change the partial pressures of the
reacting molecules)
Solubility product constant, Ksp
o Write an equation for the dissociation of a slightly soluble compound
o Write the Ksp expression
o Understand what the magnitude of the Ksp indicates
o Ba able to calculate the value of Ksp, given concentrations or molar solubility, and vice versa
Catalyst
o Speeds up a chemical reaction
o Provides an alternate pathway with lower activation energy
o Is not used up in the process of the reaction
o Enzymes are biological catalysts