Summary on Topic 2 1st LAW OF THERMODYNAMICS:

Law of Conversation of Energy

+∆𝐸𝑠𝑦𝑠𝑡𝑒𝑚 = −∆𝐸𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔
SPONTANEITY
−∆𝐸𝑠𝑦𝑠𝑡𝑒𝑚 = +∆𝐸𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔
• Spontaneous Processes – occur naturally
• Nonspontaneous Processes – occur if and “Energy can neither be created nor destroyed, it can Movement in:
only if with outside assistance/effort is done only be converted from one form of energy to Solids restricted
another.” Liquids not so restricted
“Processes that are spontaneous in one direction are Gas very free
nonspontaneous in the opposite direction.” Example: • these movements cannot be predicted (very
Example: 1. Eating food (mechanical- digestive system) >>> body random) and when they are excited
& mind being rejuvenated (chemical-absorption of collisions are made (kinetic collisions) due
1. Melting of ice in room temperature >>> vitamins) to closeness of atoms
spontaneous • if there’s movement there’s a change in
2. Mechanical Energy state
OPPOSITE: Freezing of water in refrigerator >>>
𝑀𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 = ∆𝐾𝑖𝑛𝑒𝑡𝑖𝑐 + ∆𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 = 0
nonspontaneous (refrigerator assistance)

2. Messy room >>> spontaneous - from rest to motion Entropy, S – measure of molecular randomness
OPPOSITE: Clean room >>> nonspontaneous 3. Internal Energy Solids restricted Lower randomness
(exerted effort by the room owner) Liquids not so restricted Low randomness
∆𝐸𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 = ∆𝐸𝑠𝑦𝑠𝑡𝑒𝑚 + ∆𝐸𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔 = 0
Gas very free Higher randomness
∆𝐸 = 𝑄 + 𝑊
REVERSIBLE vs. IRREVERSIBLE PROCESS Therefore, 𝑆𝑠𝑜𝑙𝑖𝑑 < 𝑆𝑙𝑖𝑞𝑢𝑖𝑑 < 𝑆𝑔𝑎𝑠
“Every spontaneous process are exothermic process is ↑ 𝑜𝑟𝑑𝑒𝑟 = ↓ 𝑆
a WRONG CONCLUSION.” 2nd LAW OF THERMODYNAMICS: ↓ 𝑑𝑖𝑠𝑜𝑟𝑑𝑒𝑟 = ↑ 𝑆
Entropy (randomness or disorder)
“Spontaneous processes are dependent on the path
• if there’s movement there’s a change in state:
taken between states.” “The state of entropy of the entire universe, as an
Solid to liquid melting/fusion
isolated system, will always increase over time.”
• Reversible Processes – we can restore the Liquid to gas vaporization ∆𝑆 > 0
system to its original condition with no Heat (Q) = travels from hot to cold surfaces Solid to gas sublimation
Work (W) = associated with expansion or shrinking of volume at Opposite reactions ∆𝑆 < 0
change to the surroundings const. pressure
• Irreversible Processes – the system and its
surroundings cannot return to its original • both heat and work are defined by the
condition random motion of molecules
Change in Entropy, ∆𝑺
At molecular level:
∆𝑆 = 𝑆𝑓𝑖𝑛𝑎𝑙 − 𝑆𝑖𝑛𝑖𝑡𝑖𝑎𝑙
“Almost all real processes are irreversible” – because
of infinitesimal (very very small) changes • atoms of solid, liquid and gases move when
subjected to change in temperature, If 𝑆𝑓 > 𝑆𝑖 , then ∆𝑆> 0 (randomness is increased)
pressure, volume and addition/subtraction of If 𝑆𝑓 < 𝑆𝑖 , then ∆𝑆< 0 (randomness is decreased)
moles. (excited state of atoms)
• Exothermic or Endothermic: ∆𝐻 - at equilibrium: (Q = K)
∆𝑆𝑠𝑢𝑟𝑟 = ±
𝑇
𝐼𝑓 ∆𝑆𝑠𝑦𝑠𝑡𝑒𝑚 > 0 𝑖𝑠 𝐸𝑛𝑑𝑜𝑡ℎ𝑒𝑟𝑚𝑖𝑐 𝑃𝑟𝑜𝑐𝑒𝑠𝑠, ∆𝐺 = ∆𝐺 ° + 𝑅𝑇 ln 𝐾 = 0
𝑡ℎ𝑒𝑛 ∆𝑆𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔 < 0 𝑖𝑠 𝐸𝑥𝑜𝑡ℎ𝑒𝑟𝑚𝑖𝑐 𝑃𝑟𝑜𝑐𝑒𝑠𝑠
∆𝐺 ° = −𝑅𝑇 ln 𝐾
𝐼𝑓 ∆𝑆𝑠𝑦𝑠𝑡𝑒𝑚 < 0 𝑖𝑠 𝐸𝑥𝑜𝑡ℎ𝑒𝑟𝑚𝑖𝑐 𝑃𝑟𝑜𝑐𝑒𝑠𝑠,
3rd LAW OF THERMODYNAMICS:
𝑡ℎ𝑒𝑛 ∆𝑆𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔 > 0 𝑖𝑠 𝐸𝑛𝑑𝑜𝑡ℎ𝑒𝑟𝑚𝑖𝑐 𝑃𝑟𝑜𝑐𝑒𝑠𝑠 ∆𝑮 Relationship Direction Spontaneity
“The entropy of a perfect crystalline substance is zero
at the absolute zero of temperature (T= 0 K).” of K & Q of rxn
> 0 (positive sign); < 0 (negative sign)
<0 K>Q Forward Spontaneous
>0 K<Q Backward Nonspontaneous
∆𝑺𝒖𝒏𝒊𝒗𝒆𝒓𝒔𝒆 = ∆𝑺𝒔𝒚𝒔𝒕𝒆𝒎 + ∆𝑺𝒔𝒖𝒓𝒓𝒐𝒖𝒏𝒅𝒊𝒏𝒈 =0 K=Q No shift Equilibrium
FREE ENERGY, ∆𝑮
∆𝑆𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 > 0 inc. entropy spontaneous ∆𝐺 = ∆𝐻 − 𝑇∆𝑆
∆𝑆𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 < 0 dec. entropy spontaneous 𝑲 𝐥𝐧 𝑲 ∆𝑮° Direction of rxn
opposite rxn >1 Positive Negative Forward
∆𝑆𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 = 0 process does At equilibrium At constant pressure and temperature: =0 0 0 No shift
not occur <1 Negative Positive Backward
“The driving force for a spontaneous process is an ∆𝐺 < 0 𝑖𝑠 𝑆𝑝𝑜𝑛𝑡𝑎𝑛𝑒𝑜𝑢𝑠
increase in the entropy of the universe.” ∆𝐺 > 0 𝑖𝑠 𝑁𝑜𝑛𝑠𝑝𝑜𝑛𝑡𝑎𝑛𝑒𝑜𝑢𝑠
∆𝐺 = 0 𝑎𝑡 𝐸𝑞𝑢𝑖𝑙𝑖𝑏𝑟𝑖𝑢𝑚

∆𝐻 ∆𝑆 ∆𝐺 Spontaneity STANDARD FREE ENERGY REACTION, ∆𝑮°

STANDARD ENTROPY OF REACTION, ∆𝑺𝒐𝒓𝒙𝒏 − + − Spontaneous at all T
∆𝐺 ° = ∑ 𝑛𝐺𝑓° (𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠) − ∑ 𝑚𝐺𝑓° (𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠)
− − +/− Spontaneous at low T
° °( °(
∆𝑆𝑟𝑥𝑛 = ∑ 𝑛𝑆 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠) − ∑ 𝑚𝑆 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠) + + +/− Spontaneous at high T
- Values for 𝐺𝑓° are found in the same table as ∆𝐻𝑓°
+ − + Nonspontaneous at all T
- Values for 𝑆 ° are found in the same table as ∆𝐻𝑓°

Example: Reactions with gases

At equilibrium: Additional input from book and ppt:
° ↑ number of gas moles
∆∆𝑆 > 0 ∆𝐺 = ∆𝐻 − 𝑇∆𝑆 = 0 1. The maximum possible useful work obtainable from a
∆𝑆 ° < 0 ↓number of gas moles
process at constant temperature and pressure is equal to
°
Small value ∆𝑆𝑟𝑥𝑛 No change in numbers of gas ∆𝐻
∆𝑆 = the change in free energy: 𝑊𝑚𝑎𝑥 = ∆𝐺
Can be (+) or (-) moles 𝑇
- But in the real-world applications: 𝑊 < 𝑊𝑚𝑎𝑥
- and energy of universe remains constant but its
Effect of Temperature on Spontaneity: When ∆𝐺 is dependent on pressure and temperature: usefulness decreases because it disperses in its
- entropy changes is highly dependent on heat flow surrounding as thermal energy (heat to cold)
∆𝐺 = ∆𝐺 ° + 𝑅𝑇 𝑙𝑛 𝑃
- heat travels from hot to cold, higher impact of heat
is observed at lower temperatures OR
2. Efficiency of heat turbines:
- important characteristics of ∆𝑆𝑠𝑢𝑟𝑟𝑜𝑢𝑛𝑑𝑖𝑛𝑔 : °
∆𝐺 = ∆𝐺 + 𝑅𝑇 𝑙𝑛 𝑄
o sign of ∆𝑆𝑠𝑢𝑟𝑟 depends on the direction of 𝑄𝐻 − 𝑄𝐶 𝑇𝐻 − 𝑇𝐶
𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = =
heat flow 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
where 𝑄 = 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑄𝐶 𝑇𝐶
o magnitude of ∆𝑆𝑠𝑢𝑟𝑟 depends on the
- 𝑄𝐻 & 𝑄𝑐 are heat energy from hot to cold temp
temperature
- 𝑇𝐻 & 𝑇𝑐 are hot to cold temp