CHM1011 Study Guide - Quiz Guide: Acid Dissociation Constant, Gibbs Free Energy, Buffer Solution

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Reactions which do not go to completion are equilibria. The reaction proceeds in both directions, denoted by a double headed arrow. Indicates the extent of a reaction- how far the forward reaction proceeded before equilibrium was established. If kc is very small, the reactants are favoured. If kc is very large, the products are favoured. For aa + bb cc + dd, kc= [(cid:2887)](cid:3161)[(cid:2888)](cid:3162) Defines the extent and direction of a reaction when the system is not at equilibrium. Can be used to determine the direction in which the reaction will proceed. When q=kc, the system is at equilibrium. If qkc, the back reaction will be favoured. If an equilibrium system is subjected to change, the system will adjust itself to partially oppose the effect of the change. An equilibrium exists in a saturated solution between the undissolved solid and its dissolved form.

Related Questions

Q2. Based below discussion and your K1 value, are the reactants or products favoured at equilibrium? discuss and explain.

In the general (balanced) reaction: aA + bB cC + dD The equilibrium constant, Kc, is equal to: Kc = [C]c [D]d [A]a [B]b where [A], [B], [C] and [D] are the equilibrium concentrations in mol/L. For complex formation we call Kc the formation or stability constant, for which we will use the symbol K and a subscript to denote the number of ligands that attach to the metal ion. The formation constant determines the extent to which a particular complex is formed. Within 'normal' concentration values (say, 0.1 M â 1 M), a very large value for K indicates that products are favoured and if K is very small the reaction lies in favour of the reactants. Some transition metal complexes have very distinct absorption spectra. In the second part of this experiment we will exploit this to estimate the equilibrium concentration of a complex, and so calculate the equilibrium constant for complex formation.

Very few chemical reactions go to completion. Instead, most reach a state called chemical equilibrium in which both products and reactants are present. The concentrations of reactants and products can be predicted using the equilibrium constant, Kc, which is a mathematical expression based on the chemical equation. For example, in the reaction

aA(aq)+bB(aq)âcC(aq)+dD(aq)

where a, b, c, and d are the stoichiometric coefficients, the equilibrium constant is

Kc=[C]c[D]d[A]a[B]b

where [A], [B], [C], and [D] are the equilibrium concentrations. If the reaction is not at equilibrium, the quantity can still be calculated, but it is called the reaction quotient, Qc, instead of the equilibrium constant, Kc.

Part A

A mixture initially contains A, B, and C in the following concentrations: [A]=0.600mol Lâ1, [B]=1.25mol Lâ1, and [C]=0.400mol Lâ1. The following reaction occurs and equilibrium is established:

A(aq)+2B(aq)âC(aq)

At equilibrium, [A]=0.450mol Lâ1 and [C]=0.550mol Lâ1. Calculate the value of the equilibrium constant, Kc .

At equilibrium, the concentrations of reactants and products can be predicted using the equilibrium constant, Kc, which is a mathematical expression based on the chemical equation. For example, in the reaction

aA + bB ? cC + dD

where a, b, c, and d are the stoichiometric coefficients, the equilibrium constant is

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

Qc=[C]tc[D]td / [A]ta[B]tb

where each concentration is measured at some arbitrary time t.

QUESTION:

A mixture initially contains A, B, and C in the following concentrations: [A] = 0.300 M , [B] = 0.750 M , and [C] = 0.550 M . The following reaction occurs and equilibrium is established:

A+2B?C

At equilibrium, [A] = 0.120 M and [C] = 0.730 M . Calculate the value of the equilibrium constant, Kc.

Express your answer numerically.

CHM1011 Study Guide - Quiz Guide: Acid Dissociation Constant, Gibbs Free Energy, Buffer Solution

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