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) R1 + R2 —> <— P1 + P2 and the concentration of R1 increases. 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) R1 + R2 —> <— P1 + P2 and the concentration of R1 increases. 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