Chemistry for the gifted and talented: entropy and equilibrium
This activity shows the students the fundamental link between entropy and equilibrium and increases students' understanding of scientific models. It highlights the importance of mathematical descriptions in physical chemistry.
Entropy and equilibrium
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Entropy and equilibrium spreadsheet
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Unit A2 1: Further Physical and Organic Chemistry
4.4 Equilibrium
4.4.1 calculate equilibrium concentrations, given suitable data;
4.4.2 calculate the numerical values, with units, for the equilibrium constant Kc, given suitable data limited to homogeneous systems;
4.2 Enthalpy, entropy, and free energy
4.2.1 recall that enthalpy change is not sufficient to explain feasible change, for example the endothermic reaction between ammonium carbonate and ethanoic acid;
4.2.2 recall that the balance between entropy change and enthalpy change determines the feasibility of a reaction;
4.2.3 recall that entropy is a measure of disorder;
4.2.4 calculate the standard entropy change, ΔSӨ, in a chemical reaction using standard entropy data;
4.2.5 use the equation ΔG = ΔH - TΔS to calculate standard free energy changes;
4.2.6 recall that processes are feasible when the free energy change is negative;
4.2.7 recall that when the enthalpy change and the entropy change have the same sign, the feasibility of the process depends on the temperature, and calculate the temperature at which these processes start or cease to be feasible;
Unit AS 2: Further Physical and inorganic Chemistry and an Introdution to Organic Chemistry
2.10 Equilibrium
2.10.3 deduce an expression for the equilibrium constant Kc and its units for a given homogeneous equilibrium system;
2.10.4 relate the magnitude of Kc to the position of equilibrium and extent of reaction;
Unit 3: PHYSICAL AND INORGANIC CHEMISTRY
3.8 Equilibrium constants
(c) significance of the magnitude of an equilibrium constant and how this relates to the position of equilibrium
3.7 Entropy and feasibility of reactions
(c) how to calculate an entropy change from absolute entropy values, ΔS = Sfinal – Sinitial
(d) concept of Gibbs free energy change and how it is calculated using the relationship, ΔG = ΔH – TΔS
(e) spontaneous reactions having a negative value for ΔG and how the effect of entropy change explains the spontaneous occurrence of endothermic processes
Gibbs free-energy change, ΔG, and entropy change, ΔS
ΔH, whilst important, is not sufficient to explain feasible change.
The concept of increasing disorder (entropy change, ΔS).
ΔS accounts for the above deficiency, illustrated by physical changes and chemical changes.
The balance between entropy and enthalpy determines the feasibility of a reaction given by the relationship: ΔG = ΔH – TΔS. For a reaction to be feasible, the value of ΔG must be zero or negative.
Students should be able to: calculate entropy changes from absolute entropy values.
Topic13: Enegetics II
Topic 13B: Entropy
12. understand that, since some endothermic reactions can occur at room temperature, enthalpy changes alone do not control whether reactions occur
13. know that entropy is a measure of the disorder of a system and that the natural direction of change is increasing total entropy (positive entropy change)
14. understand why entropy changes occur during: changes of state; dissolving of a solid ionic lattice; reactions in which there is a change in the number of moles from reactants to products
15. understand that the total entropy change in any reaction is the entropy change in the system added to the entropy change in the surroundings, shown by the expression: ΔStotal = ΔSsystem + ΔSsurroundings
16. be able to calculate the entropy change for the system, ΔSsystem , in a reaction, given the entropies of the reactants and products
18. know that the balance between the entropy change and the enthalpy change determines the feasibility of a reaction and is represented by the equation ΔG = ΔH − TΔSsystem
5.2.2 Enthalpy and entropy
a) explanation that entropy is a measure of the dispersal of energy in a system which is greater, the more disordered a system
b) explanation of the difference in magnitude of the entropy of a system: of solids, liquids and gases; and for a reaction in which there is a change in the number of gaseous molecules
c) calculation of the entropy change of a system, ΔS, and related quantities for a reaction given the entropies of the reactants and products
d) explanation that the feasibility of a process depends upon the entropy change and temperature in the system, TΔS, and the enthalpy change of the system, ΔH
e) explanation, and related calculations, of the free energy change, ΔG, as: ΔG = ΔH – TΔS (the Gibbs' equation) and that a process is feasible when ΔG has a negative value
Advanced Higher
Inorganic and Physical Chemistry
Reaction feasibility
The entropy (S) of a system is a measure of the degree of disorder of the system. The greater the degree of disorder, the greater the entropy.
Entropy increases as temperature increases. Changes of state involve changes in entropy.
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