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Chemistry HSC (Year 12) > Mod 5 EQUILIBRIUM AND ACID REACTIONS: Calculating the equilibrium constant Keq > Flashcards

Mod 5 EQUILIBRIUM AND ACID REACTIONS: Calculating the equilibrium constant Keq Flashcards

Inquiry question: How can the position of equilibrium be described and what does the equilibrium constant represent?

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1
Q

Identify what is the equilibrium constant refers to?

A

Keq is the equilibrium constant ratio of the concentrations of products to the concentration of reactants at equilibrium.

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2
Q

True or false: The only factor that affects Keq value is temperature

A

True.

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3
Q

Describe what is meant by homogeneous equilibrium

A

Equilibrium where all substances are in the same phase, whether it be gas, liquid, or solid.

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4
Q

Describe what is meant by heterogeneous equilibrium

A

Equilibrium where substances are in different phases, whether it be gas, liquid, or solid.

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5
Q

What is the correct expression for the equilibrium constant KeqKeq​ for the reaction:

aA+bB↔cC+dD

A)
Keq=[A]a[B]b/[C]c[D]d

B)
Keq=[C][D]/[A][B]

C)
Keq=[C]c[D]d/[A]a[B]

D)
Keq=[A][B]/[C][D]

A

Correct Answer: C)

Keq=[C]c[D]d/[A]a[B]

The equilibrium constant Keq for the reaction aA+bB↔cC+dD is given by the ratio of the product of the concentrations of the products raised to their stoichiometric coefficients to the product of the concentrations of the reactants raised to their stoichiometric coefficients.

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6
Q

If Keq​ is very large, approximately 1000 or more, equilibrium is to the…?

A

Equilibrium is to the right (product species are favoured).

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7
Q

If Keq is very small, approximately 0.001 or less, equilibrium is to the…?

A

Equilibrium is to the left (reactant species are favoured).

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8
Q

If Keq is close to 1 (about 0.1 - 10), equilibrium is…?

A

Equilibrium is neither to the left nor right because the concentration of both reactants and products is similar.

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9
Q

What does ICE stand for in the context of chemical equilibrium calculations?

A

ICE stands for Initial, Change, Equilibrium. It is used to organize data and solve for unknown concentrations in equilibrium problems.

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10
Q

For the reaction N2+3H2↔2NH3​, if you start with 5.89 mol of N2​ and 8.23 mol of H2​ in a 5L vessel, what are the initial concentrations of N2​ and H2​?

A

[N2​] = 5.89 mol​/5L
=1.178 mol/L

[H2] = 8.23 mol/5L
=1.646 mol/L

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11
Q

In the ICE table for the reaction N2+3H2↔2NH3, if 0.48 mol of NH3​ is formed at equilibrium in a 5L vessel, what is the equilibrium concentration of NH3​?

A

[NH3​] = 0.48 mol​/5L
=0.096 mol/L

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12
Q

In an ICE table, what do you not include in the equilibrium constant expression if present in the reaction? (Hint, states)

A

You do not include solids or liquids in the equilibrium constant expression. Only gases and aqueous species are included.

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13
Q

Why is it important to use an ICE table for equilibrium calculations when initial concentrations and equilibrium amounts are known?

A

An ICE table helps organise initial concentrations, changes in concentration, and equilibrium concentrations systematically, making it easier to solve for unknowns and calculate the equilibrium constant accurately.

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14
Q

What is the purpose of calculating the equilibrium constant Keq​ for a chemical reaction?

A

The equilibrium constant Keq indicates the ratio of the concentrations of products to reactants at equilibrium, providing insight into the position of equilibrium and the extent to which a reaction proceeds.

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15
Q

Describe what is meant by the reaction quotient (Q)

A

The reaction quotient (Q) measures the relative amounts of products and reactants present during a reaction at a particular point in time. Q is usually used to determine whether a reaction is currently at equilibrium.

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16
Q

If Q = Keq, the system…

If Q < Keq, the system…

If Q > Keq, the system…

A

The system is at equilibrium

The system needs more product, shifts to the right

The system needs more reactant, shifts to the left

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17
Q

Recall the dependency of an equilibrium constant on the equation

A

If one equation is the reverse of another, the equilibrium constant will be reciprocal (e.g if the original Keq = 20, the reverse reaction will have Keq of 1/20)

If the coefficients of an equation are doubled, the value of Keq is squared (e.g if the original Keq = 20, the doubled reaction will have Keq = 400)

If the coefficients of an equation are halved, the value of Keq is the square root of the original Keq (e.g if the original Keq = 20, the halved reaction will have Keq = √20)

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18
Q

What is the only factors that affects the value of Keq?

A

Temperature

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19
Q

What are factors that shift the position of equilibrium of Keq?

A

Pressure/volume, concentration

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20
Q

What is the general form of an exothermic reaction?

A

A + B ⇌ C + D + heat

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21
Q

In an exothermic reaction, which direction is exothermic?

A

The forward reaction is exothermic.

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22
Q

In an exothermic reaction, which direction is endothermic?

A

The reverse reaction is endothermic.

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23
Q

According to Le Chatelier’s principle, what happens to the concentration of reactants when the temperature is increased in an exothermic reaction?

A

The concentration of reactants will increase.

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24
Q

According to Le Chatelier’s principle, what happens to the concentration of products when the temperature is increased in an exothermic reaction?

A

The concentration of products will decrease.

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25
Q

What happens to the equilibrium constant (Keq) when the temperature is increased in an exothermic reaction?

A

Keq decreases.

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26
Q

In which direction does the equilibrium position shift when the temperature is increased in an exothermic reaction?

A

The equilibrium position shifts to the left (towards the reactants).

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27
Q

How does the equilibrium constant (Keq) change when the temperature is decreased in an exothermic reaction?

A

Keq increases.

28
Q

In which direction does the equilibrium position shift when the temperature is decreased in an exothermic reaction?

A

The equilibrium position shifts to the right (towards the products).

29
Q

What is an easy way to remember the relationship between temperature and Keq in exothermic reactions?

A

For exothermic reactions, temperature and Keq are inversely proportional. When temperature increases, Keq decreases, and vice versa.

30
Q

What is the general form of an endothermic reaction?

A

A + B + heat ⇌ C + D

31
Q

In an endothermic reaction, which direction is endothermic?

A

The forward reaction is endothermic.

32
Q

In an endothermic reaction, which direction is exothermic?

A

The reverse reaction is exothermic.

33
Q

According to Le Chatelier’s principle, what happens to the concentration of products when the temperature is increased in an endothermic reaction?

A

The concentration of products increases.

34
Q

According to Le Chatelier’s principle, what happens to the concentration of reactants when the temperature is increased in an endothermic reaction?

A

The concentration of reactants decreases.

35
Q

What happens to the equilibrium constant (Keq) when the temperature is increased in an endothermic reaction?

A

Keq increases.

36
Q

In which direction does the equilibrium position shift when the temperature is increased in an endothermic reaction?

A

The equilibrium position shifts to the right (towards the products).

37
Q

How does the equilibrium constant (Keq) change when the temperature is decreased in an endothermic reaction?

A

Keq decreases.

38
Q

In which direction does the equilibrium position shift when the temperature is decreased in an endothermic reaction?

A

The equilibrium position shifts to the left (towards the reactants).

39
Q

What is an easy way to remember the relationship between temperature and Keq in endothermic reactions?

A

For endothermic reactions, temperature and Keq are directly proportional. When temperature increases, Keq increases, and vice versa.

40
Q

Which ions are spectator ions in the iron(III) thiocyanate equilibrium?
Fe(NO3)3(aq) + KSCN(aq) ⇌ FeSCN2+(aq) + KNO3(aq) △H<0

A

Potassium ion (K+) and nitrate ion (NO3-).

41
Q

What is the net ionic equation for the iron(III) thiocyanate equilibrium?

A

Fe3+(aq) + SCN-(aq) ⇌ FeSCN2+(aq)

42
Q

What happens when Na2HPO4 is added to the iron(III) thiocyanate equilibrium?

A

Hydrogen phosphate ions react with Fe3+ to form FeHPO4+(aq), reducing Fe3+ concentration and shifting equilibrium to the left. The solution becomes less red and more yellow.

43
Q

What is the effect of adding KSCN crystals to the iron(III) thiocyanate equilibrium?

A

It increases the concentration of SCN-, shifting the reaction to the right. The solution becomes more red and less yellow.

44
Q

How does increasing temperature affect the iron(III) thiocyanate equilibrium?

A

It favours the reverse reaction (endothermic direction), making the solution more yellow.

45
Q

How does decreasing temperature affect the iron(III) thiocyanate equilibrium?

A

It favours the forward reaction (exothermic direction), making the solution darker red.

46
Q

What is the effect of temperature on an exothermic reaction in terms of equilibrium position?

A

Increasing temperature shifts equilibrium to the left (reverse reaction), and decreasing temperature shifts equilibrium to the right (forward reaction).

47
Q

What is dissociation in the context of ionic solutions?

A

Dissociation is the process by which ionic substances break up into positive and negative ions when they dissolve in water.

48
Q

What happens to the concentration of ions in a solution during dissociation?

A

The concentration of ions in the solution increases.

49
Q

Provide an example of a dissociation reaction for an ionic compound.

A

PbCl2(s) ⇌ Pb2+(aq) + 2Cl-(aq)

50
Q

In a dissociation reaction, where is the solid written, and why is water not included in the equation?

A

The solid is always written on the reactant side, and water is not included in the equation because it is not involved in the reaction.

51
Q

Describe the lattice structure of salts.

A

Salts consist of cations and anions held together by ionic bonds in a three-dimensional structure.

52
Q

What happens when a salt is added to water?

A

Water molecules, which are polar, are attracted to the ions in the lattice. If the force between an ion and a water molecule is greater than the forces within the crystal, the ion will separate from the crystal structure.

53
Q

Define solution equilibria.

A

Solution equilibria is the dynamic equilibrium that exists between dissolved and undissolved components of solute in a solvent (Ksp).

54
Q

What occurs when a solution exceeds its saturation point?

A

A precipitate forms, and the excess chemical remains as a solid at the bottom of the container.

55
Q

What is the relationship between Qsp and Ksp when Qsp = Ksp?

A

Saturation is reached.

56
Q

What does it mean if Qsp < Ksp?

A

Saturation has not been reached, and no precipitate will form.

57
Q

Describe the steps to predict a precipitate formation using solubility rules.

A
  1. Write a chemical equation and predict a precipitate.
  2. Write the equilibrium for dissociation.
  3. Calculate equilibrium concentrations of ions.
  4. Calculate Q.
  5. Compare Q with Ksp from the data sheet.
58
Q

What is the conclusion if Qsp < Ksp in the example calculation?

A

No precipitate will be formed.

59
Q

What defines an acid in terms of hydronium ion formation?

A

An acid forms a hydronium ion (H3O+) in aqueous solution by producing H+ ions.

60
Q

What defines a base in terms of hydronium ion reaction?

A

A base reacts with hydronium ions and contains either hydroxide ion (OH-) or oxide ion (O2-).

61
Q

How do strong acids and bases differ from weak acids and bases in water?

A

Strong acids/bases ionize completely in water and do not reach equilibrium, while weak acids/bases partially ionize and reach equilibrium.

62
Q

Provide an example of a strong acid reaction in water.

A

HCl(aq) + H2O(l) → Cl-(aq) + H3O+(aq)

63
Q

Provide an example of a weak acid reaction in water.

A

CH3COOH(aq) + H2O(l) ⇌ CH3COO-(aq) + H3O+(aq)

64
Q

What is the ionization constant (Ka) and its significance?

A

The ionization constant (Ka) indicates the strength of an acid. The greater the concentration of ionized species, the higher the Ka value, indicating a stronger acid.

65
Q

What is the ionization constant (Kb) and its significance?

A

The ionization constant (Kb) indicates the strength of a base. The greater the concentration of ionized species, the higher the Kb value, indicating a stronger base.

Chemistry HSC (Year 12) (16 decks)

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