Chemical equilibrium
Chemistry · Unit 3 — Equilibrium, acids and redox reactions · Chemical equilibrium systems
Learning objectives (54)
LO-1acid-base or conductometric titrations.LO-2Analyse data and interpret graphical representations of relative changes in the concentration of reactants and product against time, to determine the position of equilibrium. Factors that affect equilibriumLO-3Analyse data to compare the relative strengths of acids and bases. Acid-base indicatorsLO-4Analyse data to determine an appropriate indicator given the equivalence point of the titration and the pH range of the indicator (assuming indicators change colour over a range of pKa ± 1). Volumetric analysisLO-5Analyse data to determine reaction quotients (Q), equilibrium constants (Kc), the concentrations of reactants and products and the concentration of ions in aqueous solutions. Properties of acids and basesLO-6Analyse data to determine the strength, concentration, pH and electrical conductivity of acids and bases. pHLO-7Analyse titration curves to calculate the concentration of a solution with reference to a standard solution. Chem istry 2025 v1.3 The following subject matter may be assessed in the internal assessments.LO-8Analyse volumetric data, including solubility, conductometric and acid-base titration curves, to determine moles, mass, volume and concentration.LO-9Apply Kw to calculate the concentration of hydrogen ions from the concentration of hydroxide ions in a solution.LO-10Apply Le Châtelier’s principle to determine the effect changes of temperature, concentration of chemicals, pressure and the addition of a catalyst have on the position of equili brium and on the value of the equilibrium constant. Equilibrium constantsLO-11Apply Le Châtelier’s principle to explain how buffer solutions respond to the addition of hydrogen ions and hydroxide ions. Chem istry 2025 v1.3 Dissociation constantsLO-12Calculate dissociation constants (Ka, Kb, and Kw), pKa, pKb, and the concentrations of reactants and products. (Formula: 𝐾a = [H3O+][A−] [HA]; 𝐾b = [BH+][OH−] [B]; 𝐾𝑤 = 𝐾a × 𝐾b)LO-13Calculate equilibrium constants (Kc) and the concentrations of reactants and products. Assume [reactants]initial = [reactants]equilibrium when 𝐾c is very small and state assumption when used. (Formula: 𝐾c = [C]c[D]d [A]a[B]b for the reaction aA + bB ⇋ cC + dD) Chem istry 2025 v1.3LO-14Calculate pH, hydrogen ion concentration [H+(aq)], pOH and hydroxide ion concentrations [OH–(aq)] for strong acids and bases. (Formula: pH = –log10 [H+] and pOH = –log10[OH–]) Brønsted-Lowry modelLO-15Calculate solubility products (Ksp) and the concentrations of ions in aqueous solutions. (Formula: 𝐾sp = [C]c[D]d for the reaction aA(s) ⇋ cC(aq) + dD(aq))LO-16Calculate the reaction quotient (Q) for reversible reactions (Formula: Q = [C]c[D]d [A]a[B]b for the reaction aA + bB ⇋ cC + dD)LO-17Describe acids and bases in equilibrium systems using the Brønsted-Lowry model.LO-18Determine the effect of temperature change on chemical systems at equilibrium by considering the enthalpy change for the forward and reverse reactions.LO-19Determine the equilibrium law expression for homogeneous and heterogeneous systems.LO-20Determine the expression for the dissociation constant for weak acids ( Ka) and weak bases (Kb) from balanced chemical equations.LO-21Determine the extent of a reaction from the magnitude of the equilibrium constant (Kc).LO-22Determine the formula of the conjugate acid (or base) of any Brønsted-Lowry base (or acid).LO-23Discriminate between open or closed chemical systems.LO-24Discriminate between strong and weak acids and bases in terms of the extent of dissociation, rate of reaction, pH and electrical conductivity.LO-25Discriminate between the terms end point and equivalence point.LO-26Discriminate between the terms strong, weak, concentrated and dilute for acids and bases.LO-27Explain observable properties and the characteristics of physical and chemical systems in a state of equilibrium.LO-28Explain that the strength of acids is related to the degree of ionisation at equilibrium in aqueous solution.LO-29Explain that, over time, physical change and reversible chemical reactions reach a state of dynamic equilibrium in a closed system, with the relative concentrations of products and reactants defining the position of equilibrium.LO-30Explain the Brønsted-Lowry model using chemical equations that illustrate the transfer of hydrogen ions (protons) between conjugate acid-base pairs.LO-31Explain the effect of changes of temperature, concentration and pressure on chemical systems at equilibrium by applying collision theory to the forward and reverse reactions.LO-32Explain the relationship between the pH range, the end point and the pKa value of an acid-base indicator.LO-33Explain the reversibility of chemical reactions by considering the activation energies of the forward and reverse reactions.LO-34factors that affect equilibrium (Le Châtelier’s principle)LO-35Identify acids as monoprotic, diprotic or polyprotic.LO-36Identify carboxylic and carbonic acids as weak acids and ammonia and amines as weak bases.LO-37Identify hydrochloric, nitric and sulfuric acid as strong acids and group 1 hydroxides and barium hydroxide as strong bases.LO-38Identify that acid-base indicators are a weak acid or a weak base where the conjugate acid - base pair have different colours and can be represented by HIn(aq) ⇋ H+(aq) + In−(aq) or BOH(aq) ⇋ B +(aq) + OH−(aq).LO-39Identify that acids are substances that can act as proton (hydrogen ion) donors.LO-40Identify that amphiprotic species can act as Brønsted-Lowry acid (or base).LO-41Identify that buffers are solutions that are conjugate in nature and resist a change in pH when a small amount of an acid or base is added. (Buffer calculations are not required.)LO-42Identify that indicators change colour when pH = pKa.LO-43Identify that physical changes are usually reversible, whereas only some chemical rea ctions are reversible.LO-44Identify that the equilibrium constant (Kc) indicates the relationship between product and reactant concentrations at equilibrium.LO-45Identify that the solubility product (Ksp) gives a measure of the solubility of an ionic compound.LO-46Identify that the strength of acids can be represented with chemical equations and equilibrium constants (Ka).LO-47Identify that water is a weak electrolyte and the self-ionisation of water is represented by Kw. (Formula: Kw = [H+][OH–])LO-48Infer shifts in equilibrium reactions using equilibrium constants (Kc) and reaction quotients (Q).LO-49Interpret acid-base titration curves to determine the intercept with pH axis, equivalence point, buffer region and points where pKa = pH or pKb = pOH.LO-50Interpret conductometric titration curves to determine the intercept with conductivity axis, equivalence point and volume of titrant.LO-51properties of acids and basesLO-52Sketch the general shapes of conductometric and acid-base titration curves involving strong and weak acids and bases. (Titration of weak acids to weak bases is not required.)LO-53solubilityLO-54Symbolise equilibrium equations using ⇋ in balanced chemical equations.
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