Chemical Equilibrium Concepts and Applications

What is chemical equilibrium?

A dynamic process in which concentrations of reactants and products remain constant over time, with the rate of the forward reaction equal to the rate of the reverse reaction.

What is the Law of Mass Action?

The ratio of concentrations or partial pressures of products to reactants at equilibrium has a characteristic value at a given temperature.

What is the equilibrium constant (K)?

A unitless value representing the ratio of concentration (or partial pressure) terms in the equilibrium constant expression at a specific temperature.

What is the equilibrium constant expression for a general reaction aA(g) + bB(g) ⇌ cC(g) + dD(g)?

K = [C]^c [D]^d / [A]^a [B]^b, where [X] represents concentration.

How do you express the equilibrium constant for the reverse reaction?

For the reverse reaction, Kreverse = 1/Kforward.

What distinguishes homogeneous equilibria from heterogeneous equilibria?

Homogeneous equilibria involve reactants and products in the same phase, while heterogeneous equilibria involve reactants and products in more than one phase.

Provide an example of a homogeneous equilibrium reaction.

H2O(g) + CO(g) ⇌ H2(g) + CO2(g) is an example of homogeneous equilibrium.

Provide an example of a heterogeneous equilibrium reaction.

CaCO3(s) ⇌ CaO(s) + CO2(g) is an example of heterogeneous equilibrium.

What is the significance of solids and liquids in heterogeneous equilibria?

The concentrations of solids and liquids are constant at a given temperature and do not affect the equilibrium.

What is Le Châtelier's Principle?

It states that if an external change is applied to a system at equilibrium, the system will adjust to counteract that change and restore a new equilibrium.

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

Changing the concentration of reactants or products will shift the equilibrium position to favor the side that reduces the change.

How does pressure affect equilibrium in gaseous reactions?

Increasing pressure shifts the equilibrium towards the side with fewer moles of gas, while decreasing pressure shifts it towards the side with more moles.

How does temperature affect equilibrium?

Increasing temperature shifts the equilibrium in the endothermic direction, while decreasing temperature shifts it in the exothermic direction.

What is the relationship between Kc and Kp?

Kp is the equilibrium constant for partial pressures, related to Kc by the equation Kp = Kc(RT)^(Δn), where Δn is the change in the number of moles of gas.

What is the equilibrium constant expression for the reaction 2 SO2(g) + O2(g) ⇌ 2 SO3(g)?

Kc = [SO3]^2 / ([SO2]^2 [O2]).

What is the equilibrium constant expression for the reverse reaction of 2 SO3(g) ⇌ 2 SO2(g) + O2(g)?

Kc = [SO2]^2 [O2] / [SO3]^2.

How do you express Kc for the reaction 2NO2(g) ⇌ NO(g) + NO3(g)?

Kc = [NO][NO3] / [NO2]^2.

What is the equilibrium constant expression for NO3(g) ⇌ NO(g) + O2(g)?

K'c = [NO][O2] / [NO3].

How can K''c be expressed in terms of Kc and K'c for the reaction NO3(g) ⇌ NO(g) + O2(g)?

K''c = Kc * K'c.

What is the significance of calculating equilibrium concentrations?

Calculating equilibrium concentrations allows for the prediction of the amounts of reactants and products at equilibrium, which is essential for understanding reaction dynamics.

What is the effect of temperature changes on equilibrium mixtures?

Temperature changes can shift the equilibrium position, favoring either the forward or reverse reaction depending on whether the reaction is exothermic or endothermic.

What is the equilibrium constant expression for the reaction 2 NO2 (g) ⇌ 2 NO(g) + O2(g)?

K = [NO]^2[O2] / [NO2]^2.

What does a K value greater than 1 indicate about a reaction at equilibrium?

It indicates that there are more product molecules than reactant molecules, favoring products.

What does a K value less than 1 imply about a reaction at equilibrium?

It implies that there are more reactant molecules than product molecules, favoring reactants.

How do you calculate the equilibrium constant Kc for the reaction 2 SO2(g) + O2(g) ⇌ 2 SO3(g) at 800 K?

Kc = [SO3]^2 / ([SO2]^2[O2]).

What are the equilibrium concentrations given for the reaction 2 SO2(g) + O2(g) ⇌ 2 SO3(g) at 800 K?

[SO2] = 3.0 x 10^-3 M, [O2] = 3.5 x 10^-3 M, [SO3] = 5.0 x 10^-2 M.

What is the equilibrium constant Kc for the reaction N2(g) + 3H2(g) ⇌ 2NH3(g) at 500°C?

Kc = 0.0603.

What is the relationship between Kp and Kc for a reaction?

Kp = Kc(RT)Δn, where Δn is the change in moles of gas.

How is Δn calculated for the reaction 4NH3(g) + 7O2(g) ⇌ 4NO2(g) + 6H2O(g)?

Δn = (4 + 6) - (4 + 7) = -1.

What is the value of Kp if Kc = 4.00 at 425°C for the reaction PCl5(g) ⇌ PCl3(g) + Cl2(g)?

Kp = (4.00) x (0.0821 x 698) = 229.

What does the reaction quotient Q represent?

Q is the numerical value of the mass action expression for any concentrations or partial pressures of reactants and products.

What does it mean if Q < K for a reaction?

It means the reaction will proceed toward the products.

What does it mean if Q = K for a reaction?

It indicates that the reaction is at equilibrium.

What does it mean if Q > K for a reaction?

It means the reaction will proceed toward the reactants.

Is the reaction CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) at equilibrium with Kc = 5.6 and concentrations 0.100M, 0.200M, 0.500M, 0.800M?

Calculate Q and compare with Kc to determine if at equilibrium.

What is the equilibrium constant Kc for the reaction 2 NO(g) + O2(g) ⇌ 2 NO2(g) at 500 K?

Kc = 6.9 x 10^5.

What concentrations were present in a 5.0 L vessel at 500 K for the reaction 2 NO(g) + O2(g) ⇌ 2 NO2(g)?

0.060 mol of NO, 1.0 mol of O2, and 0.80 mol of NO2.

How do you determine if a reaction is at equilibrium using the reaction quotient Q?

Compare Q with K; if Q does not equal K, the reaction is not at equilibrium.

What is the ideal gas law equation?

PV = nRT, where P is pressure, V is volume, n is moles, R is the gas constant, and T is temperature.

What is the value of the gas constant R in the ideal gas law?

R = 0.0821 L·atm/(K·mol).

What is the equilibrium constant expression for the reaction 2H2O(l) ⇌ 2H2(g) + O2(g)?

Kc = [H2]^2[O2] / [H2O]^2, but Kc is not defined for pure liquids.

What is the equilibrium constant expression for the reaction SiCl4(g) + 2 H2(g) ⇌ Si(s) + 4 HCl(g)?

Kc = [HCl]^4 / [SiCl4][H2]^2, but Kc is not defined for solids.

What is the purpose of a RICE table in chemical equilibrium calculations?

To organize the reaction, initial concentrations, changes, and equilibrium concentrations.

What does the 'C' in the RICE table represent?

Changes in concentrations or pressures as the system moves to equilibrium.

What does K represent in the context of chemical reactions?

The equilibrium constant, which indicates the ratio of concentrations of products to reactants at equilibrium.

When is the 5% rule applicable in equilibrium calculations?

When the equilibrium constant is very small and the initial concentrations of reactants are relatively large.

What is the equilibrium concentration approximation for reactants when using the 5% rule?

The equilibrium concentration of a reactant can be approximated as its initial concentration if the change (x) is less than 5% of that initial concentration.

How do you calculate the initial concentration of HI in Problem 11?

Initial [HI] = 0.500 mol / 2.00 L = 0.250 M.

What happens to the equilibrium position when CO2 is removed from the reaction H2O(g) + CO(g) ⇌ H2(g) + CO2(g)?

The reaction shifts to the right (toward products) to establish a new equilibrium.

How does an increase in pressure affect gaseous equilibria?

The reaction shifts to the side with fewer moles of gas.

In the reaction 2NO2(g) ⇌ N2O4(g), what happens if the volume is decreased?

The reaction shifts to the right toward products (N2O4) due to increased pressure.

What is the equilibrium constant Kc for the reaction N2O4(g) ⇌ 2 NO2(g) at 25 °C?

4.64 x10-3.

How do you calculate equilibrium concentrations for the reaction 2HI(g) ⇌ H2(g) + I2(g) with Kc = 0.11?

Set up an ICE table and solve for equilibrium concentrations using the initial concentration and Kc.

What is the initial concentration of N2O4 in Problem 12?

0.050 M.

What is the initial concentration of N2O4 and NO2 in Problem 13?

[N2O4] = 0.0200 M and [NO2] = 0.0300 M.

What is the effect of decreasing the volume on the equilibrium of a reaction?

It increases the partial pressures of gases, potentially shifting the equilibrium position.

What does Q represent in relation to K?

Q is the reaction quotient, which compares the current concentrations of products and reactants to K.

What does it mean if Q < K?

The reaction will shift to the right (toward products) to reach equilibrium.

What is the initial concentration of HI in Problem 10?

0.100 M.

What is the significance of the equilibrium constant being very small?

It indicates that the position of equilibrium favors the reactants.

What happens to the equilibrium concentrations when the system is subjected to stress?

The system will shift to relieve the stress, either by favoring products or reactants.

What is the equilibrium concentration of H2 and I2 when 0.500 mol of HI is added to a 2.00 L container?

Calculate using the ICE table and Kc value.

What is the relationship between initial concentrations and equilibrium concentrations when using approximations?

If the change in concentration is small, the equilibrium concentration can be approximated as the initial concentration.

What is the equilibrium expression for the reaction CO(g) + H2O(g) ⇌ CO2(g) + H2(g)?

Moles of products remain the same, ∆n = 0, no shift.

What happens to the equilibrium position when the moles of products increase in the reaction 2CO(g) ⇌ C(s) + CO2(g)?

The reaction shifts to the right because ∆n = -1.

What happens to the equilibrium position when the moles of products decrease in the reaction 2CO(g) ⇌ C(s) + CO2(g)?

The reaction shifts to the left because ∆n = 1.

How does increasing temperature affect the equilibrium of an exothermic reaction like N2(g) + 3H2(g) ⇌ 2NH3(g)?

The reaction shifts to the left, decreasing the amount of NH3.

What is the effect of adding heat to an exothermic reaction on the equilibrium constant K?

K decreases.

What is the effect of removing heat from an exothermic reaction on the equilibrium constant K?

K increases.

How does increasing temperature affect the equilibrium of an endothermic reaction?

The reaction shifts to the right, increasing the amount of products.

In the reaction N2(g) + O2(g) ⇌ 2NO(g) with ΔH° = +182.6 kJ, how does the equilibrium change with increased temperature?

NO increases, while N2 and O2 decrease.

What happens to the amount of ethyl acetate when the temperature is increased in its equilibrium reaction with acetic acid and ethanol?

The amount of ethyl acetate increases.

How does the equilibrium constant Kc change when the temperature is increased for an endothermic reaction?

Kc increases.

How does the equilibrium constant Kc change when the temperature is decreased for an endothermic reaction?

Kc decreases.

What does Le Châtelier's principle state about the effect of temperature on equilibrium?

Increasing temperature shifts the equilibrium position in the direction that absorbs heat.

What can be concluded about the reaction A(g) + B(s) ⇌ AB(g) at different temperatures?

The reaction is endothermic since more product is formed at higher temperatures.

What is the effect of adding a catalyst to a chemical equilibrium?

It speeds up the rate of reaching equilibrium without changing K or equilibrium concentrations.

In the reaction 2CO(g) + O2(g) ⇌ 2CO2(g) with ΔH° = -566 kJ, what happens to CO when a platinum catalyst is added?

The amount of CO remains the same.

What happens to the equilibrium when the temperature is increased for the reaction 2CO(g) + O2(g) ⇌ 2CO2(g)?

The amount of CO decreases.

What happens to the equilibrium when the pressure is increased by decreasing the volume for the reaction 2CO(g) + O2(g) ⇌ 2CO2(g)?

The amount of CO decreases.

How does the equilibrium constant Kc relate to the rate constants kf and kr?

At equilibrium, kf[A][B] = kr[C][D].

In the reaction NO(g) + O3(g) ⇌ NO2(g) + O2(g), which rate constant is larger if Kc is very high?

kf is larger than kr.

What is the value of kr at 300 K if kf is 8.5 x 106 M-1s-1 and Kc is 3.4 x 10^34?

kr = kf / Kc = 8.5 x 10^6 / 3.4 x 10^34.

How do the values of kf and kr change when the temperature is lowered from 300 K to 230 K?

Both kf and kr decrease.