Equilibrium

Roadmap

What is Equilibrium?

Equilibrium constant

Equilibrium expression

Calc Kc from [eqm]

Manipulating Kc

Q

prediction perturb

La Chatelier

Eqm calculations

7.1.NoS1 Obtaining evidence for scientific theories—isotopic labelling and its use in defining equilibrium. (1.8)

7.1.NoS2 Common language across different disciplines—the term dynamic equilibrium is used in other contexts, but not necessarily with the chemistry definition in mind. (5.5)

7.1.U1 A state of equilibrium is reached in a closed system when the rates of the forward and reverse reactions are equal.

7.1.U2 The equilibrium law describes how the equilibrium constant (Kc) can be determined for a particular chemical reaction.

7.1.U3 The magnitude of the equilibrium constant indicates the extent of a reaction at equilibrium and is temperature dependent.

7.1.U4 The reaction quotient (Q) measures the relative amount of products and reactants present during a reaction at a particular point in time. Q is the equilibrium expression with non-equilibrium concentrations. The position of the equilibrium changes with changes in concentration, pressure, and temperature.

7.1.U5 A catalyst has no effect on the position of equilibrium or the equilibrium constant.

7.1.AS1 The characteristics of chemical and physical systems in a state of equilibrium.

7.1.AS2 Deduction of the equilibrium constant expression (K_{c}) from an equation for a homogeneous reaction.

7.1.AS3 Determination of the relationship between different equilibrium constants (Kc) for the same reaction at the same temperature.

7.1.AS4 Application of Le Châtelier’s principle to predict the qualitative effects of changes of temperature, pressure and concentration on the position of equilibrium and on the value of the equilibrium constant.

7.1.G1 Physical and chemical systems should be covered.

7.1.G2 Relationship between Kc values for reactions that are multiples or inverses of one another should be covered.

7.1.G3 Specific details of any industrial process are not required.

7.1.IM1 The Haber process has been described as the most important chemical reaction on Earth as it has revolutionized global food production. However, it also had a large impact on weaponry in both world wars.

7.1.ToK1 Scientists investigate the world at different scales; the macroscopic and microscopic. Which ways of knowing allow us to move from the macroscopic to the microscopic?

7.1.ToK2 Chemistry uses a specialized vocabulary: a closed system is one in which no matter is exchanged with the surroundings. Does our vocabulary simply communicate our knowledge; or does it shape what we can know?

7.1.ToK3 The career of Fritz Haber coincided with the political upheavals of two world wars. He supervised the release of chlorine on the battlefield in World War I and worked on the production of explosives. How does the social context of scientific work affect the methods and findings of science? Should scientists be held morally responsible for the applications of their discoveries?

7.1.Uz1 Square brackets are used in chemistry in a range of contexts: eg concentrations (topic 1.3), Lewis (electron dot) structures (topic 4.3) and complexes (topic 14.1).

7.1.Aims1 Aim 6: Le Châtelier’s principle can be investigated qualitatively by looking at pressure, concentration and temperature changes on different equilibrium systems.

7.1.Aims2 Aim 7: Animations and simulations can be used to illustrate the concept of dynamic equilibrium.

7.1.Aims3 Aim 8: Raise awareness of the moral, ethical, and economic implications of using science and technology. A case study of Fritz Haber can be used to debate the role of scientists in society.

17.1.NoS Employing quantitative reasoning—experimentally determined rate expressions for forward and backward reactions can be deduced directly from the stoichiometric equations and allow Le Châtelier’s principle to be applied. (1.8, 1.9)

17.1.U1 Le Châtelier’s principle for changes in concentration can be explained by the equilibrium law

17.1.U2 The position of equilibrium corresponds to a maximum value of entropy and a minimum in the value of the Gibbs free energy

17.1.U3 The Gibbs free energy change of a reaction and the equilibrium constant can both be used to measure the position of an equilibrium reaction and are related by the equation, ∆G = −RT lnK .

17.1.AS1 Solution of homogeneous equilibrium problems using the expression for Kc.

17.1.AS2 Relationship between ∆G and the equilibrium constant.

17.1.AS3 Calculations using the equation ∆G = −RT lnK.

17.1.G1 The expression ∆G = −RT lnK is given in the data booklet in section 1.

17.1.G2 Students will not be expected to derive the expression ∆G = −RT lnK.

17.1.G3 The use of quadratic equations will not be assessed

17.1.ToK1 The equilibrium law can be deduced by assuming that the order of the forward and backward reaction matches the coefficients in the chemical equation. What is the role of deductive reasoning in science?

17.1.ToK2 We can use mathematics successfully to model equilibrium systems. Is this because we create mathematics to mirror reality or because the reality is intrinsically mathematical?

17.1.ToK3 Many problems in science can only be solved when assumptions are made which simplify the mathematics. What is the role of intuition in problem solving?

17.1.Uz1 The concept of a closed system in dynamic equilibrium can be applied to a range of systems in the biological, environmental and human sciences.

17.1.Aims1 Aim 6: The equilibrium constant for an esterification reaction and other reactions could be experimentally investigated.

17.1.Aims2 Aim 7: The concept of a dynamic equilibrium can be illustrated with computer animations.