Equilibrium

What is equilibrium in a chemical reaction?

A state where the forward and reverse reaction rates are equal, and the concentrations of all reactants and products remain constant over time.

How does equilibrium appear macroscopically and microscopically?

Macroscopically static (nothing seems to happen), but microscopically dynamic (molecules are constantly changing).

What is represented by a Rate vs. Time graph at equilibrium?

Equilibrium is reached when the lines representing forward and reverse reactions meet.

What does an Amount (concentration) vs. Time graph show at equilibrium?

Equilibrium is reached when the lines plateau.

What happens to the concentrations of reactants and products as equilibrium is established?

The concentrations of reactants decrease while the concentrations of products increase until they reach constant values.

Define homogeneous equilibria.

Equilibria that involve reactants and products in the same phase.

Define heterogeneous equilibria.

Equilibria that involve reactants and products in different phases.

What is the equilibrium constant (K)?

A value that describes the relationship between reactants and products in a system at equilibrium, calculated from concentrations or pressures.

What types of substances are included in the equilibrium constant expression?

Only aqueous and gaseous substances; solids and liquids are excluded.

What does a large value of K (K >> 1) indicate?

The equilibrium mixture contains mostly products.

What does a small value of K (K << 1) indicate?

The equilibrium mixture contains mostly reactants.

How is the equilibrium constant affected by reversing a reaction?

The equilibrium constant for the reverse reaction is the reciprocal of the original constant (K_reverse = 1/K_original).

What happens to K if the balanced equation is multiplied by a factor of n?

The equilibrium expression for the new reaction is the original expression raised to the nth power (K_new = (K_original)^n).

What is the reaction quotient (Q)?

A measure of the relative amounts of reactants and products at any point in time, used to determine if a system is at equilibrium.

What does it mean if Q < K?

The reaction will shift to the product side to reach equilibrium.

What does it mean if Q > K?

The reaction will shift to the reactant side to reach equilibrium.

What is Le Chatelier's Principle?

If a stress is applied to a system at equilibrium, the system will adjust to minimize that stress.

How does concentration affect equilibrium according to Le Chatelier's Principle?

Adding a component shifts the equilibrium away from that component, while removing it shifts the equilibrium toward it.

How does temperature affect equilibrium?

K changes with temperature; for endothermic reactions, heat is a reactant, and for exothermic reactions, heat is a product.

What is the effect of increasing pressure on a gaseous equilibrium?

The equilibrium shifts toward the side with fewer moles of gas.

What is the effect of adding an inert gas to a system at equilibrium?

It does not affect the equilibrium position.

What happens to the equilibrium position if the temperature of an exothermic reaction is increased?

The equilibrium shifts to the left, favoring the reactants.

What is the equilibrium expression for the reaction H2(g) + I2(g) ↔ 2HI(g)?

K = [HI]^2 / ([H2][I2]).

How do you determine if a reaction is at equilibrium?

Compare Q to K; if Q equals K, the system is at equilibrium.

What is the significance of the equilibrium constant value?

It indicates whether the forward or reverse reaction is favored.

What is the goal of the Rainbow Lab?

To make a test tube rainbow using different equilibrium systems.

What determines the dominant species in an equilibrium reaction?

The side of the reaction that is favored indicates the major species.

What is the reaction for the formation of carbon monoxide?

CO2(g) + C(graphite) ↔ 2CO(g) with ∆H=+172.5kJ.

What is the effect of temperature on the formation of carbon monoxide?

A high temperature is more favorable for the formation of carbon monoxide.

What is the effect of pressure on the formation of carbon monoxide?

A low pressure is more favorable for the formation of carbon monoxide.

What is the molarity of Fe3+ in a 0.24M solution of Fe2(SO4)3?

0.48M.

What is solubility equilibrium?

The dynamic process where a solid is simultaneously dissolving and precipitating.

What does Ksp stand for?

Solubility product constant, which describes the concentrations of dissolved ions at saturated equilibrium.

What is the relationship between Ksp value and solubility?

The smaller the Ksp value, the lower the solubility.

Write the dissolution equation and Ksp expression for CaO.

CaO(s) ↔ Ca2+ + O2-; Ksp = [Ca2+][O2-].

Calculate Ksp from solubility data for Ag2CO3 with a solubility of 1.2x10-4 M.

Ksp = [2.4x10-4]²[1.2x10-4] = 6.9x10-12.

How do you calculate molar solubility from Ksp?

Set Ksp = [Ba2+][SO42-] and solve for x, where x is the molar solubility.

What is the common ion effect?

The presence of a common ion lowers the solubility of a compound.

What happens to the solubility of CaF2 when Ca2+ is added?

The equilibrium shifts left, favoring solid formation and decreasing solubility.

What is the Ksp expression for AgCl?

Ksp = [Ag+][Cl-].

What does it mean if Q < Ksp?

No precipitate will form.

What does it mean if Q > Ksp?

A precipitate will form.

Determine if a precipitate will form when 0.01 mol of Na2CrO4 is added to 225 mL of 1.5x10-4 M AgNO3.

Yes, a precipitate will form since Q > Ksp.

How do you find the new molarities when mixing solutions?

Use the dilution formula M1V1 = M2V2.

What is the Ksp of PbCl2?

Ksp = 1.7 x 10-5.

What is the solubility of BaSO4 in a 1.5 M Na2SO4 solution?

7.3x10-11 M.

How do you calculate the solubility of Al(OH)3 in 0.040 M Ba(OH)2?

x = 5.86 x 10-31 M.

What is the significance of Ksp in precipitation reactions?

Ksp helps determine if a precipitate will form based on ion concentrations.

What is the molar solubility of silver sulfate if Ksp = 1.4x10-5?

1.5x10-2 M.

What happens to the solubility of a salt when a common ion is added?

The solubility decreases due to the shift in equilibrium.

What is the formula for the reaction quotient (Q) in precipitation reactions?

Q = [Pb2+][Cl-]^2

How do you determine the molar concentrations of ions after mixing solutions?

Calculate total volume and then use initial concentrations to find final concentrations.

What is the Ksp value for Mg(OH)2?

9.0 x 10^-12.

What happens when a saturated solution of PbI2 is prepared?

The concentrations of Pb2+ and I- can be calculated using Ksp.

What is the equilibrium expression for the reaction 2POCl3(g) ↔ 2PCl3(g) + O2(g)?

Keq = [PCl3]^2[O2] / [POCl3]^2

What does ICE stand for in ICE boxes?

Initial, Change, Equilibrium.

When should you use an ICE box?

When you are given initial values before equilibrium.

How do you calculate Keq from equilibrium concentrations?

Plug the equilibrium concentrations into the equilibrium expression.

What is the equilibrium constant (Kc) for the decomposition of HI at 458°C if 0.442 mol I2 is present?

Calculate using the initial and equilibrium concentrations of HI, H2, and I2.

What is the effect of increasing temperature on an endothermic reaction?

The equilibrium shifts to favor the products.

How do you determine the direction of a reaction to reach equilibrium?

Calculate Q and compare it to K.

What is the Ksp value for BaCrO4?

1.2 x 10^-10.

What happens to the concentration of Pb2+ when NaI is added to a saturated solution of PbI2?

The concentration of Pb2+ decreases due to the common ion effect.

What is the molar solubility of Cd(OH)2 in a 0.34M solution of KOH?

Calculate using the Ksp value of Cd(OH)2.

What is the significance of a K value much smaller than 1?

It indicates that the reactants are favored at equilibrium.

How do you find equilibrium concentrations when given K and initial concentrations with variables?

Set up an ICE box and solve for x.

What is the equilibrium concentration of Br2 if [HBr]=0.35 M and [H2]=0.22 M at equilibrium?

Use the equilibrium expression K = [HBr]^2 / ([H2][Br2]).

What happens to the partial pressure of C if the temperature is increased in an endothermic reaction?

The partial pressure of C increases.

What is the initial concentration of H2 and I2 if both are 0.010 mol/L?

0.010 mol/L each.

What is the K value for the reaction CO2(g) ↔ 2CO(g) if the initial pressure of CO2 is 2 atm?

Calculate using the equilibrium expression.

What is the effect of adding a solid to a saturated solution on ion concentrations?

The concentrations of dissolved ions remain unchanged.