THERMODYNAMICS Flashcards
1st Law of Thermodynamics
Energy cannot be created or destroyed.
INTERNAL ENERGY of an ISOLATED system is CONSTANT.
ΔE = E(FINAL) – E(INITIAL)
EXOTHERMIC
____ enthalpy
Heat transfer TO surroundings
-ΔH
Bonds formed are STRONGER than broken.
ENDOTHERMIC
___ enthalpy
Reaction requires/absorbs heat
+ΔH
Bonds formed are WEAKER than broken.
OPEN SYSTEM
Exchanges matter & energy with surroundings
CLOSED system
Exchanges energy with the surroundings (not matter)
ISOLATED system
neither energy nor matter exchanged with surroundings
STATE functions
value depends only on present state of system, not path used to arrive
EXPANSION WORK equation
w = F x d
ENTHALPY (H)
ΔH =
ΔH =
Heat change during a reaction at constant pressure.
State function.
ΔH = H (products) – H (reactants) ΔH = H (Bond BREAKING) - H (MAKING) ΔH = ΔE + PΔV
Enthalpy of FUSION
Heat required to melt a substance without changing its temp.
Enthalpy of VAPORISATION
Heat required to vaporise a substance without changing temp.
Enthalpy of SUBLIMATION
Heat required to convert a substance from solid to gas directly.
CALORIMETRY
Measure HEAT FLOW at CONSTANT
(A) PRESSURE, ΔH.
(B) VOLUME, ΔE
Heat capacity (C)
Heat required to raise the temp. of a substance by a specific amount.
q = C x ΔT
Molar Heat Capacity (Cm)
Heat required to raise temp. of 1 mol of substance by 1 C.
q = Cm x mols x ΔT
Specific Heat Capacity
Heat required to raise the temp. pf 1g substance by 1 C.
q = C m ΔT
Hess’ Law
Overall ENTHALPY change is the sum of all the individual steps of the reaction.
ΔH = ΔH1 + ΔH2
Standard Enthalpy of Formation ΔH
Heat change when 1 mol of compound forms from its elements under standard conditions.
Standard enthalpy of formation of an element in its standard state =
0
= ΔH products - ΔH reactants
Bond dissociation energy
energy required to break a chemical bond of a molecule in its gaseous state & energy released when the bond forms.
Bond enthalpy values depend on
Bond order
Electronic environment of atoms comprising a bond.
IN GASEOUS PHASE
Bond enthalpy =
Bond enthalpy = ΔH reactant - ΔH product bonds
Standard enthalpy of Combustion
ΔH per mol of combustible substance.
ΔH
Heat change in a reaction at constant pressure.
ΔS
Amount of freedom of motion / randomness in a system.
State function
SPONTANEOUS reaction:
_ΔH, _ΔS
-ΔH, +ΔS
NON-SPONTANEOUS reaction:
_ΔH, _ΔS
+ΔH, -ΔS
ΔS =
ΔS = S(FINAL) - S(INITIAL)
ΔS=q(rev)/T
= heat reversibly transfered to substance / temp. (ENTROPY OF HEATING WATER)
2nd law of thermodynamics
entropy of the universe INCREASES in a spontaneous process.
3rd law of thermodynamics
entropy of a perfectly ordered crystalline substance at 0K is ZERO.
ATOMS ARE STATIONARY at absolute zero
-> ZERO ENTROPY.
ENTROPY is greatest in gases and less in solids.
T or F
T
SPONTANEOUS PROCESS: ΔS(universe) =
EQUILIBRIUM: ΔS(universe) =
ΔS(universe) = ΔS(sys) + ΔS(sur) > 0 ΔS(universe) = ΔS(sys) + ΔS(sur) = 0
Standard molar entropy
entropy of 1 mol of pure substance at 1 atm & specified temp.
Bond DISSOCIATION (breaking) is a ___thermic process
ENDO
Bond ASSOCIATION (making) is a ___thermic process
EXO
State the equation for bond enthalpies relating bond dissociation & association
ΔH = H (BOND BREAKING) – H (BOND MAKING)
SPONTANEOUS process
_ΔH, _ΔS
-ΔH, +ΔS
NON-SPONTANEOUS
_ΔH, _ΔS
+ΔH, -ΔS
ENTROPY, S
Measure of freedom of motion / randomness / DISORDER in a system
Compare the entropy of solid, liquid, and gaseous states
S(SOLID)
Relate entropy and heat reversibly transferred to a substance.
ΔS = q REV / T
SPONTANEOUS processes:
ΔS(UNIV) = ΔS(SYS) __ ΔS(SUR) __ 0
ΔS(UNIV) = ΔS(SYS) + ΔS(SUR) > 0
EQUILIBRIUM processes:
ΔS(UNIV) = ΔS(SYS) __ ΔS(SUR) __ 0
ΔS(UNIV) = ΔS(SYS) + ΔS(SUR) = 0
Standard molar entropy
entropy of 1 mol of pure substance at 1 atm pressure and a specified temp.
Standard entropy of reaction
entropy change for a reaction at 1 atm and 25 C.
RELATE G, H, T and S.
ΔG = ΔH – TΔS
SPONTANEOUS
_ΔS
_ΔG
+ΔS
-ΔG
NON-SPONTANEOUS:
_ΔS
_ΔG
- ΔS
+ ΔG
EQUILIBRIUM
_ΔS
_ΔG
ΔS = 0 ΔG = 0
What does IC50 measure
INHIBITOR POTENCY: inhibitor conc which reduces enzymatic activity by 50%.
EXERGONIC
_ΔG
Reaction releases more energy than it consumes.
-ΔG
ENDERGONIC
_ΔG
Reaction consumes more energy than it releases.
+ΔG
