Revision check:
You need to be able to:
a) Demonstrate an understanding that, since endothermic reactions can occur spontaneously at room temperature, enthalpy changes alone do not control whether reactions occur
b) Demonstrate an understanding of entropy in terms of the random dispersal of molecules and of energy quanta between molecules
c) Demonstrate an understanding that the entropy of a substance increases with temperature, that entropy increases as solid → liquid → gas and that perfect crystals at zero Kelvin (absolute zero) have zero entropy
d) Demonstrate an understanding that the standard entropy of a substance depends mainly on its physical state but also on its complexity
e) Demonstrate an understanding that reactions occur due to chance collisions, and that one possible ordered arrangement, e.g. in a crystalline solid, can be rearranged into many possible disordered arrangements, e.g. in a solution, so the probability of disorder is greater than order
f) Interpret the natural direction of change as being in the direction of increasing total entropy (positive entropy change), e.g. gases spread spontaneously through a room
g) Carry out experiments and relate the results to disorder and enthalpy changes including:
i. Dissolving a solid, e.g. adding ammonium nitrate crystals to water
ii. Gas evolution, e.g. reacting ethanoic acid with ammonium carbonate
iii. Exothermic reaction producing a solid, e.g. burning magnesium ribbon in air
iv. Endothermic reaction of two solids, e.g. mixing solid barium hydroxide, Ba(OH)2.8H2O with solid ammonium chloride
h) Demonstrate an understanding that the entropy change in any reaction is made up of the entropy change in the system added to the entropy change in the surroundings, summarized by the expression: ΔStotal = ΔSsystem + ΔSsurroundings
i) Calculate the entropy change in the system for a reaction, ΔSsystem, given entropy data
j) Use the expression ΔSsurroundings = -ΔH/T to calculate the entropy change in the surroundings and hence ΔStotal
k) Demonstrate an understanding that the feasibility of a reaction depends on the balance between ΔSsystem and ΔSsurroundings, and that at higher temperatures the magnitude of ΔSsurroundings decreases and its contribution to ΔStotal is less. Reactions can occur as long as ΔStotal is positive even if one of the other entropy changes is negative
l) Demonstrate an understanding of and distinguish between the concepts of thermodynamic stability and kinetic inertness
m) Understand that endothermic reactions can occur spontaneously at room temperature
n) Define the term enthalpy of hydration of an ion and use it and lattice energy to calculate the enthalpy of solution of an ionic compound
o) Demonstrate an understanding of the factors that affect the values of enthalpy of hydration and the lattice energy of an ionic compound
p) Use entropy and enthalpy of solution values to predict the solubility of ionic compounds.
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