Notes Chemical equilibrium Flashcards by Sbongumenzi Constantia

What happens to chemical reactions before they are complete?

They often seem to stop but are actually reversible.

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What is chemical equilibrium?

It is the state reached by a reaction mixture when the rates of the forward and reverse reactions have become equal.

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In a reversible reaction, what do the original reactants form?

Products, which can react to give back the original reactants.

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What does the graph of a chemical reaction approaching equilibrium show?

How the amounts of reactants and products change.

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What is the ICE table used for in chemical equilibrium?

To organize the initial, change, and equilibrium amounts of substances.

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What are the initial amounts of PCl5, PCl3, and Cl2 in the given equilibrium problem?

1.00 mol PCl5, 0 mol PCl3, 0 mol Cl2.

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What is the equilibrium amount of PCl3 in the given example?

0.135 mol.

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How do you calculate the moles of PCl5 at equilibrium if 0.135 mol of PCl3 is produced?

Moles PCl5 = 1.00 - 0.135 = 0.87 mol.

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What is the equilibrium constant expression for a reaction?

It is obtained by multiplying the concentrations of products and dividing by the concentrations of reactants.

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What is the equilibrium constant, Kc?

The value obtained for the Kc expression when equilibrium concentrations are substituted.

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What is the Kc expression for the reaction 2H2(g) + CO(g) ⇌ CH3OH(g)?

Kc = [CH3OH] / ([H2]^2[CO]).

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What does Kc use for its calculations?

Molar concentrations.

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How do you find the value of Kc at equilibrium for the decomposition of CO2?

Use an ICE table to determine the changes in moles and substitute into the Kc expression.

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What is the value of Kc for the reaction 2CO2(g) ⇌ 2CO(g) + O2(g) at equilibrium?

Kc = 0.82.

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In a heterogeneous equilibrium, how are the concentrations of solids and pure liquids treated?

They are constant and incorporated into the value of Kc.

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What happens to the Kc expression when a reaction is reversed?

The equilibrium constant expression is inverted.

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What happens to the Kc expression when the reaction is doubled?

The equilibrium constant expression is squared.

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Fill in the blank: The equilibrium constant expression for aA + bB ⇌ cC + dD is Kc = _______.

[C]^c[D]^d / [A]^a[B]^b.

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True or False: The concentration of a solid or pure liquid is included in the Kc expression.

False.

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What does the term ‘stoichiometric’ refer to in the context of chemical reactions?

The proportional relationship between reactants and products in a balanced chemical equation.

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

K = (C^c * D^d) / (A^a * B^b)

K represents the equilibrium constant, and the concentrations are raised to the power of their coefficients.

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How are Kc and Kp related?

Kp = Kc * (RT)^(Δn)

Δn is the change in moles of gas, defined as (moles of gaseous products - moles of gaseous reactants).

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What does it indicate when Kc is very large (>10^2)?

The equilibrium mixture is mostly products.

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What does it indicate when Kc is very small (<10^-2)?

The equilibrium mixture is mostly reactants.

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When Kc approaches 1, what does the equilibrium mixture contain?

Appreciable amounts of both reactants and products.

What is the reaction quotient, Q?

Q has the same form as Kc but uses concentrations at any given time.

When Kc > Q, what direction does the reaction proceed?

To the right.

When Kc < Q, what direction does the reaction proceed?

To the left.

What happens when Kc = Q?

The reaction is at equilibrium.

How is Kp calculated for a reaction CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g) at 227°C?

Kp = Kc * (RT)^(Δn) ## Footnote For this reaction, Δn = 1 (2 products - 4 reactants).

What is the value of Kp at 500 K if Kc = 0.0952?

Kp = 1.60 × 10^2.

What can we determine using the value of the equilibrium constant Kc?

* Describe the content of the reaction mixture * Determine the direction of the reaction * Calculate equilibrium concentrations given initial concentrations

If Kc = 0.82 for a reaction, what can you say about the composition of the equilibrium mixture?

There will be substantial amounts of both reactants and products.

What occurs if the partial pressure of CO is 100 mmHg and Kp = 700 at 1500 K?

The reaction will proceed forward.

Calculate the concentration of NO in an equilibrium mixture containing 0.040 M N2 and 0.010 M O2 when K = 1.0 × 10^-30.

[NO] = 2.0 × 10^-17 M.

What does ICE stand for in the context of equilibrium?

Initial, Change, Equilibrium.

What must be done when the Kc expression is not a perfect square?

Rearrange the equation to fit the quadratic format: ax^2 + bx + c = 0.

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

Kc = [H2][I2] / [HI]^2.

What is the initial concentration of HI if 0.50 mol is placed in a 5.0-L flask?

0.10 M.

What are the equilibrium concentrations of H2 and I2 when Kc = 0.016?

[H2] = [I2] = 0.010 M.

What is the quadratic format for rearranging the Kc expression?

ax² + bx + c = 0

What is the equilibrium reaction for the decomposition of N2O4?

N2O4(g) ⇌ 2NO2(g)

At 100°C, what is the Kc value for the equilibrium reaction of N2O4 decomposing to NO2?

0.36

If a 1.00-L flask initially contains 0.100 M N2O4, what must be calculated to find the equilibrium concentration of NO2?

Use the ICE table

What does the ICE table stand for in equilibrium calculations?

Initial, Change, Equilibrium

In the ICE table for the reaction N2O4(g) ⇌ 2NO2(g), what are the initial concentrations?

N2O4: 0.100 M, NO2: 0 M

What is the equilibrium concentration of NO2 if x = 0.06?

0.12 M

What is the Kc expression for the reaction H2(g) + F2(g) ⇌ 2HF(g)?

Kc = [HF]² / ([H2][F2])

For the reaction H2(g) + F2(g) ⇌ 2HF(g), what is the initial concentration in a 1.500-L vessel with 3.000 mol of each species?

2.000 M

What happens to the equilibrium position when a substance that is part of the equilibrium is added?

The equilibrium shifts to consume it.

When a substance that is part of the equilibrium is removed, what is the effect on the equilibrium?

The equilibrium shifts to produce more of it.

According to Le Châtelier’s Principle, what happens when the system is disturbed by a change in temperature, pressure, or concentration?

The system shifts in equilibrium composition to counteract the change.

What will happen to the equilibrium when Cl2 gas is added to the reaction COCl2(g) ⇌ CO(g) + Cl2(g)?

The reaction shifts to the left (reverse direction).

What is the effect on the equilibrium when the volume of the reaction container is increased?

The reaction will shift toward the side with more gas molecules.

When the total pressure in a reaction container increases, what is the expected shift in equilibrium?

The reaction will shift toward the side with fewer gas molecules.

How does changing the temperature affect the equilibrium constant?

It changes the value of the equilibrium constant.

What is the significance of ΔHo in relation to equilibrium shifts?

It determines the direction of the shift when temperature changes.

If both sides of an equilibrium reaction have the same number of moles of gas, what is the effect of pressure on the equilibrium?

Pressure has no effect on the equilibrium.

What is the equilibrium concentration of H2 and F2 if x = 1.53 in the reaction H2(g) + F2(g) ⇌ 2HF(g)?

0.47 M

What is the equilibrium concentration of HF if x = 1.53 in the reaction H2(g) + F2(g) ⇌ 2HF(g)?

5.06 M

What is the relationship between changes in partial pressure and shifts in equilibrium?

Handled like adding or removing a substance.

What will happen to the equilibrium of CO(g) + 2H2(g) ⇌ CH3OH(g) when the volume of the container is increased?

The reaction shifts to the left (reverse direction).

In the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what direction will the reaction shift when the volume is increased?

The reaction shifts to the left (reverse direction).

In the reaction COCl2(g) ⇌ CO(g) + Cl2(g), what direction will the reaction shift when the volume is increased?

The reaction shifts to the right (forward direction).

What happens to the value of the equilibrium constant when the temperature changes?

It changes ## Footnote Changing the temperature can also cause a shift in the equilibrium.

For an endothermic reaction, what is the sign of ΔH°?

ΔH° > 0 (positive) ## Footnote Heat is considered a reactant in this case.

For an exothermic reaction, what is the sign of ΔH°?

ΔH° < 0 (negative) ## Footnote Heat is considered a product in this case.

What effect does increasing temperature have on Kc for an endothermic reaction?

Increases the value of Kc ## Footnote Decreasing the temperature has the opposite effect.

What effect does increasing temperature have on Kc for an exothermic reaction?

Decreases the value of Kc ## Footnote Increasing the temperature decreases the value of Kc.

When heat is added to a reaction at equilibrium, in which direction does the equilibrium shift?

Shifts to use up heat ## Footnote This typically means the reaction shifts forward for endothermic reactions.

When heat is removed from a reaction at equilibrium, in which direction does the equilibrium shift?

Shifts to produce heat ## Footnote This typically means the reaction shifts backward for endothermic reactions.

For the reaction 2H2O(g) ⇌ 2H2(g) + O2(g) with ΔH° = 484 kJ, is it favorable at high or low temperatures?

Favorable at high temperatures ## Footnote The reaction shifts forward when heat is added.

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

Speeds up both forward and reverse reactions equally ## Footnote It does not influence the composition of the equilibrium mixture.

What does a suitable catalyst do in a reaction?

Shortens the time to reach equilibrium ## Footnote A catalyst speeds up the rate of reaction without being consumed.

In the Fischer–Tropsch process, what is synthesized?

Petrol (octane) ## Footnote The process involves carbon monoxide and hydrogen over an iron–cobalt catalyst.

What happens to the equilibrium when octane is removed from the system?

Shifts forward (to the right) ## Footnote This is because the reaction produces octane.

What direction does the equilibrium shift when the pressure is increased in the Fischer–Tropsch process?

Shifts forward (to the right) ## Footnote The reaction shifts to the side with fewer gas molecules.

Notes Chemical equilibrium Flashcards

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