Topic 12Entropy and Energetics
--King
考点一：Introduction to entropy.12.1understand that,since endothermic reactions can occur spontaneously at room temperature,enthalpy changes alone do not control whether reactions occur
12.2understand entropy as a measure of disorder of a system in terms of the random dispersal of molecules and of energy quanta between molecules
12.3understand that the entropy of a substance increases with temperature ,that entropy increases as solid →liquid →gas and that perfect crystals at zero kelvin have zero entropy
12.4
be able to interpret the natural direction of change as being in the direction of increasing total entropy (positive entropy change ),including gases spread spontaneously through a room
1,Most chemical reactions are exothermic,since substances with less energy (energetically stable )is favourable.But not all the spontaneous reactions are exothermic.The driving forces are （-enthalpy;H
-entropy;S ）
2,Entropy(熵)is a measure of the disorder/randomness of a system.The more disordered the particles are,the higher the entropy is.--Entropy of a substance increases with number of molecules .
解释：the higher number of molecules,the higher number of possible arrangements,--Entropy of a substance increases with temperature.
解释：the higher the temperature,the more energy a substance has.The more ways
to distribute energy.
Entropy :
solid →liquid →gas
Third Law of Thermodynamics(热力学第三定律)--A perfect crystals at zero kelvin have zero entropy.考点二：Total entropy.
12.6
understand that the total entropy change of any reaction is the sum of the entropy change of the system and the entropy
change of the surroundings ,summarised by the expression:
∆S total =∆S system +∆S surroundings
12.7
be able to calculate the entropy change of the system for a reaction,∆S system,given the entropies of the reactants and products
12.8
be able to calculate the entropy change in the surroundings ,and hence ∆S total,using the expression
12.9
understand that the feasibility of a reaction depends on:
i the balance between ∆S system and ∆S surroundings,so that even endothermic reactions can occur spontaneously at room temperature
ii temperature,as higher temperatures decrease the magnitude of ∆S surroundings so its contribution to ∆S total is less
12.10understand that reactions can occur as long as ∆S total is positive even if one of the other entropy changes is negative 12.11
understand and distinguish between the concepts of thermodynamic stability and kinetic stability
1,Total entropy
If a total entropy change increases (ΔStotal ＞0),the total reaction will be spontaneous .
2,The entropy change of the system
如果是enthalpy ：Δr H =the sum of Δf H (products)–the sum of Δf H (reactants)
分别把S system 和S surrounding 求出来，相加!!
都是后面减前面!!
3,The entropy change in the surroundings
4,Feasibility of a reaction
ΔS total will be positive if:
occur to
•bothΔSs urroundings andΔSs urroundings are positive
•ΔSs urroundings is positive andΔS system is negative,but the magnitude ofΔSs urroundings>the magnitude ofΔS system
•ΔSs urroundings is negative andΔS system is positive,but the magnitude ofΔSs urroundings<the magnitude ofΔS system
5,The magnitude ofΔS surrounding is depend on the temperature of surrounding.
考点三：more about entropy.
1，Entropy changes occur during:
i changes of state
solid<liquid<gas
ii dissolving of a solid ionic lattice
Dissolving a solid also increases its entropy-dissolved particles can move freely as they no longer held in one place.
iii change in the number of moles from reactants to products
The more particles you’ve got,the more ways they and their energy can be arranged.
2，Dissolving depends on the balance between the change in entropy of the solution and the change in entropy of the surroundings.
The value ofΔS total,and hence the solubility of the solid,depends on the values of three factors:
•the entropy change of the system,ΔS system
•the enthalpy change of solution,Δsol H
•the temperature,in kelvin,of the water,T.
3，solubility trend in group2
ΔS system和ΔS surrounding越来
越正；ΔS total越来越正（越
来越溶）
考点三：lattice energy
12.12
be able to define the terms:
i standard enthalpy change of atomisation ,∆at H
ii electron affinity
iii lattice energy (as the exothermic process for the formation of one mole of an
ionic solid
from its gaseous ions)
12.13be able to construct Born-Haber cycles and carry out related calculations 12.14
understand that a comparison of the experimental lattice energy value (from a
Born-Haber cycle)with the theoretical value
(obtained from electrostatic theory)in a particular compound indicates the degree of covalent bonding
1,definition
i standard enthalpy change of atomisation,∆at H
The enthalpy of atomisation is the enthalpy change when 1mole of gaseous atoms is formed from the
element in its standard state.
ii electron affinity,EA
The first electron affinity is the enthalpy change when 1mole of electrons are added to 1mole of neutral
gaseous atoms to form 1mole of gaseous 1–ions
iii lattice energy (as the exothermic process for the formation of one mole of an ionic solid from its gaseous ions)
The standard lattice energy,ΔLE H ,is the energy change when 1mole of an ionic solid is formed from its gaseous ions under standard conditions.
The first ionisation energy of an element is the energy needed to remove one electron from each atom in one mole of gaseous atoms of the element under standard conditions.
ΔS system 越来越正；ΔS surrounding 越来越负(并且幅度更大！)；ΔS total 越来越
负（越来越不溶）

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