The direction that spontaneous change is the direction in i beg your pardon total entropy increases. Total entropy change, also called the entropy adjust of the universe, is the sum of the entropy readjust of a system and the its surroundings:

DSuniv = DSsys + DSsurr

According to the second law that thermodynamics, the entropy of the universe, Suniv must always increase for a spontaneous process, the is, DSuniv>0.

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Free energy and complimentary Energy Change—the Gibbs complimentary energy, G, is offered to describe the spontaneity of a process.

G = H - TDS

The free energy change, DG is equal to -TDSuniv and also it applies just come a device itself, without regard because that the surroundings. That is defined by the Gibbs equation:


For a spontaneous procedure at constant temperature and also pressure, DG must be negative. In many cases, we have the right to predict the sign of indigenous the indications of DH and DS.Standard complimentary Energy Change, DGo —the standard complimentary energy change, DGo deserve to be calculated (1) through substituting conventional enthalpies and entropies the reaction and a Kelvin temperature into the Gibbs equation or (2) by combine standard free energies of development through the expression


Summary the Gibbs cost-free energy

Enthalpy change

Entropy change

Gibbs complimentary energy




depends ~ above T, may be + or -

yes, if the temperature is high sufficient



always negative

always spontaneous



depends on T, might be + or -

yes, if the temperature is low enough



always positive

never voluntary


1) In the Haber process for the produce of ammonia


Enthalpy change

Entropy change

N2 + 3H2


ΔH = -93Kj / mol

ΔS = -198 j / mol K

At what temperature will certainly the reaction above become spontaneous?

The fact that both terms are negative way that the Gibbs cost-free energy equation is balanced and temperature dependent:


ΔG = -93000 - (T x -198) note that the enthalpy is provided in kilojoules

if ΔG = 0 then the system is at the limit of reaction spontaneity

When ΔG = 0 then (T x -198) = -93000

and T = 93000/198 Kelvin

therefore the reaction i do not care spontaneous when T = 469 K (196 ºC)

below this temperature the reaction is spontaneous.

2) recognize the Delta G under standard problems using Gibbs free Energies that Formation uncovered in a perfect Thermodynamics table for the complying with reaction:

4HCN(l) + 5O2(g) ---> 2H2O(g) + 4CO2(g) + 2N2(g)

examine to make sure the equation is well balanced Look increase the Standard complimentary Energy of formation of H2O(g) and multiply by its coefficient(2) in the equation.

2 mole ( -237.2 kj/mole) = -474.4 kj = Standard cost-free Energy of development for 2 moles H2O(l)

Look for the Standard free Energy of formation of CO2(g) and also multiply through its coefficient (4)

4 moles ( -394.4 kj/mole) = -1577.6 kJ = Standard totally free Energy of development for 4 moles CO2

Look increase the Standard free Energy of formation of N2(g) and multiply by its coefficient(2)

2 moles(0.00 kj/mole) = 0.00 kJ = Standard free Energy of formation for 2 moles of N2(g)

add the results of steps 2,3, and 4 to acquire the Standard cost-free Energy for the products

(-474.4 kJ) + (-1577.6 kJ) + 0.00 = -2052 kJ = Standard complimentary Energy for commodities

Look increase the Standard free Energy of formation for HCN(l) and also multiply through its coefficient(4)

4 mole ( 121 kj/mole) = 484 kJ = Standard totally free Energy because that 4 mole HCN(l)

Look increase the Standard free Energy of development of O2(g) and also multiply through its coefficient(5)

5 moles (0.00 kJ/mole) = 0.00 kJ = Standard totally free Energy that 5 mole of O2(g)

add the results of measures 7 and 8 to obtain the Standard complimentary Energy the the reactants

(484) + (0.00) = 484 kJ = Standard totally free Energy for Reactants

Subtract the an outcome of action 9 from the result of step 5 to get the Standrad complimentary Energy adjust for the Reaction

Sum of complimentary Energy of assets - amount of totally free Energy of reaction = (-2052 kJ) - (484 kJ) = -1568 kJ = Standard free Energy change for the Reaction.

3) for the complying with reaction using the Thermodynamics table:

CoCl2(g) ---> CO(g) + Cl2(g)

calculation at 127°C the DG calculation the Temperature once the over reaction is in ~ equilibrium (DG = 0) at what temperature will this reaction it is in spontaneous? inspect to view if the equation is balanced identify the Delta H that the Reaction making use of Hess Summation Law and Standard Enthalpies of development

Delta H = amount of Delta Hf of commodities - sum Delta Hf of reactants

Delta H = < 1(-110.5) + 1(0.00)> - < 1(-220)>

Delta H = -110.5 - (-220) = +110.5 kJ

recognize Delta S because that the reaction using conventional Molar Entropies and Hess law of Summation

Delta S = sum Standard Molar Entropies of products - amount of traditional Molar Entropies of reactants

Delta S = < 1 mole(197.5 J/mole-K) + 1 mole(223) J/mole-K> - < 1 mole(283.7 J/mole-K)>

Delta S = 420.5 J/K - 283.7 J/K = 136.8 J/K

transform Delta S native J/K come kJ/K

136.8 J/K X 1 kJ / 1000 J = 136.8 / 1000 = .1368 kJ/K

transform 127 C come K

K = C + 273 = 127 + 273 = 400 K

Plug outcomes of step 2 and 4 into Gibbs Helmholtz Equation along with Kelvin Temperature to acquire Delta G the the Reaction

Delta G = Delta H - T(Delta S)

Delta G = 110.5 kJ - 400 K(.1368 kj/K)

Delta G = 110.5 - 54.72 kJ = + 55.78 kJ

Because this reaction has actually a confident Delta G it will be non-spontaneous as written.

Name of types Delta Hf(kJ/mole) Delta Gf(kJ/mole) S(J/mole-K)

CO2(g) -393.5 -394.4 213.7

CH3OH(l) -238.6 -166.2 127

COCl2(g) -220 -206 283.7

CO(g) -110.5 -137.2 197.5

C2H2(g) 227 209 200.9

Cl2(g) 0 0 223

H2O(g) -241.8 -228.6 188.7

H2O(l) -285.8 -237.2 69.9

HNO3(aq) -206.6 -110.5 146

N2(g) 0 0 191.5

NO2(g) 33.2 51 239.9

NO(g) 90.3 86.6 210.7

O2(g) 0 0 205

CS2 151

H2 0 0 130.6

CH4 -74.8 -50.8 186.3

H2S -20.17 -33.01 205.6

SO2 248.1

Free Energy and Equilibrium.

Because DG is a measure up of how favorable a reaction is, it likewise relates come the equilibrium constant.

A reaction through a an unfavorable DG, is really favorable, for this reason it has actually a big K. A reaction with a optimistic DG is not favorable, so it has a small K. A reaction v DG = 0 is in ~ equilibrium. There room several different DG"s. The is vital to distinguish in between them. DGo (a delta G, with a superscript o), is the complimentary energy change for a reaction, with everything in the standard states (gases in ~ 1 bar, and solutions at 1 M concentration), and also at a details temperature (usually 25°C) DG (just delta G). This is the cost-free energy readjust for a reaction that is not at the typical state. The DG"s are connected as follows. Recognize THIS EQUATION and understand exactly how to use it:

DG =DGo + RT ln Q

Where Q is the exact same Q we offered for calculating equilibrium (K is the special situation for Q when at equilibrium.)

Spontaneity and also Speed the Reactions.

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This section just points out that over there is not any direct relationship in between DG and the rate of a reaction (kinetics).


Starting through the adjust in totally free energy at constant temperature: DG° = DH° - TDS°, and with the relation in between DG and also equilibrium constant, K: DG° = -RT lnK, derive a straight equation the expresses lnK as a function of 1/T (a straight equation is of the kind y = mx + b).

(b) The equilbrium constants for the conversion of 3-phosphoglycerate come 2-phosphoglycerate at pH 7 is provided: