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Holt Chemistry Chapter 14: Chemical Equilibrium

Holt Chemistry Chapter 14: Chemical Equilibrium

14.1 Reversible Reactions and Equilibrium

  • During a completion reaction, reactants form products 
    • When one reactant is completely used, the reaction will stop 
  • During reversible reactions, reactants form products. Then the products reform reactants
  • Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal
    • To reach chemical equilibrium, the rate of the forward reaction will slow down over time. The rate of the reverse reaction will speed up.
  • Static equilibrium is a state where nothing changes. This happens because the rate of the forward reaction and the reverse reaction are equal to 0.
    • Completion reactions have static equilibrium
  • In dynamic equilibrium, there is no net change in the system 
    • The rate of the forward and reverse reactions are greater than 0 in dynamic equilibrium
    • Reversible reactions have dynamic equilibrium 
    • There is no change in the amount of products and reactants when equilibrium is reached 
  • When the arrows are the same length it means equilibrium is occurring 
  • When the arrow pointing to the products is longer, it means there is a higher quantity of products. It is said that the products are favored 
  • When the arrow pointing to the reactants is longer, there is a higher quantity of reactants. It is said that the reactants are favored 
  • Complex ion is the name given to any metal atom or ion that is bonded to more than ion atom, ion, or molecule 
    • Complex ions are also called coordination compounds 
    • Complex ions must include transition metals 
    • Complex ions will display colors 
    • The portion that is bonded to the metal is called a ligand 
    • Ligands must have unshared electrons on the central atom in order to bond to the metal portion 
    • If the ligand is a molecule, it does not have a charge 
  • [Co(NH3)6]3+ is an example of a complex ion 
  • Co3+ is the metal 
  • NH3 is the ligand 
  • 3+ is the total charge 

14.2 Systems at Equilibrium 


  • Keq is the symbol for the equilibrium constant
    • The equilibrium constant is temperature dependent, therefore there are different values at different temperatures
    • It is a ratio comparing the concentrations of reactants to the concentrations of the products in a reversible reactions
    • It must be found experimentally 
  • Keq shows of the reaction is “favorable” 
    • A reaction is favorable if there are more products then reactants 
    • Keq > 1 then there are more product particles than reactant particles 
    • The larger the number, the closer the reaction is to being a completion reaction 
    • Keq < 1 then there are more reactant particles 
    • Keq = 1 then there is a 50:50 mixture of particles 
    • It is very rare that Keq will equal 1 
  • A generic equilibrium constant equation will look like this: aA + bB —> <— cC + dD
  • In the equation above, the lowercase letters represent coefficients. The uppercase letters represent different substances 
  • A equilibrium expression will look like this: [C]c[D]d / [A]a[B]b
  • When writing the equilibrium expression, do NOT include solids and pure liquids. You do not include them because they do not express enough change.
  • Keq values do not get units 
  • Ksp is a special type of equilibrium constant 
    • It is the solubility product constant 
    • It is used to determine the solubility of “insolvable” ionic compounds. It will show how much of a substance will dissolve compared to how much will stay solid when placed in H2O
  • All ionic compounds will dissolve a little bit, even when classified as insoluble 
  • A larger Ksp means the compound is more soluble

14.3 Equilibrium Systems and Stress 

  • Le Châtelier’s Principle states when a system at equilibrium is disturbed, the system adjusts in a way to reduce the change.
  • Factors that change equilibrium are called stresses 
  • Stresses include changes in concentration, temperature, and pressure 
    • If there is a change in pressure, it will only effect reactions that have at least one gas 
  • Shifts are the response to the change 
  • A shift right will increase the length of the product arrow  
  • A shift left will increase the length of the reactant arrow 
  • Concentration 
    • An increase in concentration will cause a shift away from the compound being increased 
    • A decrease in concentration will cause a shift toward the compound being decreased 
    • The Keq will be the same value once equilibrium is reestablished 
    • Ex) R+ R2 —> <— P1 + Pand the concentration of Rincreases. The shift will be away from R1, so the product arrow will increase in length 
  • Temperature 
    • An increase in temperature will cause a shift away from the energy/heat in the reaction 
    • A decrease in temperature will cause a shift toward the energy/heat in the reaction 
    • Temperature will cause the Keq to be a value different from the original 
    • Ex) 2NO2(g) —> <— N2O4(g) + 55.3kJ and heat is decreased. The shift would be toward the heat source, so a shift right 
  • Pressure
    • Only effects reactions with gases 
    • If a reaction does not have any gases, there will be no change 
    • Keq will be the same value after equilibrium is reestablished 
    • If there is an increase in pressure, there will be a shift away from the side with the most amount of moles of gas 
    • If there is a decrease in pressure, there will be a shift toward the side with the most amount of moles of gas 
    • If the amount of moles of gas is the same on both sides, then there is no change 
    • Ex) 2NOCl(g) —> <— 2NO(g) + Cl2(g) and there is an increase in pressure. The products side has more moles, so the shift is toward the left 
  • The common ion effect is when a substance is added to the reaction and either forms a precipitate or reduces ionization 
    • It is easiest to think of the common ion effect as a change in concentration 
    • If a compound/ion is added that increases the concentration of a substance already present in the reaction, the reaction will shift to lessen the concentration 
    • If an ion is added that decreases concentration(because of the formation of a precipitate), the reaction will shift to increase the concentration 
  • There are three steps to figure out the shifts 
  • Is the compound soluble in water?
    • If the answer is no, then there is no shift in equilibrium 
    • If the answer is yes, go to the next bullet point
  • Will the substance being added increase the concentration of a substance already present in the reaction?
    • If the answer is yes, the reaction will shift in order to decrease the concentration 
    • If the answer is no, go to the next bullet point
  • Will the ions bond with other ions present in the reaction?
    • If the answer is no, there will be no shift in equilibrium 
    • If the answer is yes, a precipitate will form. The reaction will the shift to increase the concentration of the substance being used to form the precipitate

Holt Chemistry Chapter 14: Chemical Equilibrium

14.1 Reversible Reactions and Equilibrium

  • During a completion reaction, reactants form products 
    • When one reactant is completely used, the reaction will stop 
  • During reversible reactions, reactants form products. Then the products reform reactants
  • Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal
    • To reach chemical equilibrium, the rate of the forward reaction will slow down over time. The rate of the reverse reaction will speed up.
  • Static equilibrium is a state where nothing changes. This happens because the rate of the forward reaction and the reverse reaction are equal to 0.
    • Completion reactions have static equilibrium
  • In dynamic equilibrium, there is no net change in the system 
    • The rate of the forward and reverse reactions are greater than 0 in dynamic equilibrium
    • Reversible reactions have dynamic equilibrium 
    • There is no change in the amount of products and reactants when equilibrium is reached 
  • When the arrows are the same length it means equilibrium is occurring 
  • When the arrow pointing to the products is longer, it means there is a higher quantity of products. It is said that the products are favored 
  • When the arrow pointing to the reactants is longer, there is a higher quantity of reactants. It is said that the reactants are favored 
  • Complex ion is the name given to any metal atom or ion that is bonded to more than ion atom, ion, or molecule 
    • Complex ions are also called coordination compounds 
    • Complex ions must include transition metals 
    • Complex ions will display colors 
    • The portion that is bonded to the metal is called a ligand 
    • Ligands must have unshared electrons on the central atom in order to bond to the metal portion 
    • If the ligand is a molecule, it does not have a charge 
  • [Co(NH3)6]3+ is an example of a complex ion 
  • Co3+ is the metal 
  • NH3 is the ligand 
  • 3+ is the total charge 

14.2 Systems at Equilibrium 


  • Keq is the symbol for the equilibrium constant
    • The equilibrium constant is temperature dependent, therefore there are different values at different temperatures
    • It is a ratio comparing the concentrations of reactants to the concentrations of the products in a reversible reactions
    • It must be found experimentally 
  • Keq shows of the reaction is “favorable” 
    • A reaction is favorable if there are more products then reactants 
    • Keq > 1 then there are more product particles than reactant particles 
    • The larger the number, the closer the reaction is to being a completion reaction 
    • Keq < 1 then there are more reactant particles 
    • Keq = 1 then there is a 50:50 mixture of particles 
    • It is very rare that Keq will equal 1 
  • A generic equilibrium constant equation will look like this: aA + bB —> <— cC + dD
  • In the equation above, the lowercase letters represent coefficients. The uppercase letters represent different substances 
  • A equilibrium expression will look like this: [C]c[D]d / [A]a[B]b
  • When writing the equilibrium expression, do NOT include solids and pure liquids. You do not include them because they do not express enough change.
  • Keq values do not get units 
  • Ksp is a special type of equilibrium constant 
    • It is the solubility product constant 
    • It is used to determine the solubility of “insolvable” ionic compounds. It will show how much of a substance will dissolve compared to how much will stay solid when placed in H2O
  • All ionic compounds will dissolve a little bit, even when classified as insoluble 
  • A larger Ksp means the compound is more soluble

14.3 Equilibrium Systems and Stress 

  • Le Châtelier’s Principle states when a system at equilibrium is disturbed, the system adjusts in a way to reduce the change.
  • Factors that change equilibrium are called stresses 
  • Stresses include changes in concentration, temperature, and pressure 
    • If there is a change in pressure, it will only effect reactions that have at least one gas 
  • Shifts are the response to the change 
  • A shift right will increase the length of the product arrow  
  • A shift left will increase the length of the reactant arrow 
  • Concentration 
    • An increase in concentration will cause a shift away from the compound being increased 
    • A decrease in concentration will cause a shift toward the compound being decreased 
    • The Keq will be the same value once equilibrium is reestablished 
    • Ex) R+ R2 —> <— P1 + Pand the concentration of Rincreases. The shift will be away from R1, so the product arrow will increase in length 
  • Temperature 
    • An increase in temperature will cause a shift away from the energy/heat in the reaction 
    • A decrease in temperature will cause a shift toward the energy/heat in the reaction 
    • Temperature will cause the Keq to be a value different from the original 
    • Ex) 2NO2(g) —> <— N2O4(g) + 55.3kJ and heat is decreased. The shift would be toward the heat source, so a shift right 
  • Pressure
    • Only effects reactions with gases 
    • If a reaction does not have any gases, there will be no change 
    • Keq will be the same value after equilibrium is reestablished 
    • If there is an increase in pressure, there will be a shift away from the side with the most amount of moles of gas 
    • If there is a decrease in pressure, there will be a shift toward the side with the most amount of moles of gas 
    • If the amount of moles of gas is the same on both sides, then there is no change 
    • Ex) 2NOCl(g) —> <— 2NO(g) + Cl2(g) and there is an increase in pressure. The products side has more moles, so the shift is toward the left 
  • The common ion effect is when a substance is added to the reaction and either forms a precipitate or reduces ionization 
    • It is easiest to think of the common ion effect as a change in concentration 
    • If a compound/ion is added that increases the concentration of a substance already present in the reaction, the reaction will shift to lessen the concentration 
    • If an ion is added that decreases concentration(because of the formation of a precipitate), the reaction will shift to increase the concentration 
  • There are three steps to figure out the shifts 
  • Is the compound soluble in water?
    • If the answer is no, then there is no shift in equilibrium 
    • If the answer is yes, go to the next bullet point
  • Will the substance being added increase the concentration of a substance already present in the reaction?
    • If the answer is yes, the reaction will shift in order to decrease the concentration 
    • If the answer is no, go to the next bullet point
  • Will the ions bond with other ions present in the reaction?
    • If the answer is no, there will be no shift in equilibrium 
    • If the answer is yes, a precipitate will form. The reaction will the shift to increase the concentration of the substance being used to form the precipitate