 Because entropy is a state function, the property is what it is regardless of pathway, the entropy change for a given reaction can be calculated by taking the difference between the standard entropy values of products and those of the reactants.   S o reaction =  n p  S o products -  n r  S o reactants

 Calculating  S o.  Calculate  S o at 25 o C for the reaction 2NiS(s) + 3O 2 (g)  2SO 2 (g) + 2NiO(s)

Calculate  S o for the reaction of aluminum oxide by hydrogen gas: Al 2 O 3 (s) + 3H 2 (g)  2Al(s) + 3H 2 O(g)

 Standard free energy (  G o ) is the change in the free energy that will occur if the reactants in their standard states are converted to the products in their standard states.  The value of  G o tells nothing about the rate of a reaction, only its eventual equilibrium position.

 Calculating  G o as a State Function.   G o =  H o - T  S o  Consider the reaction 2 SO 2 (g) + O 2 (g)  2SO 3 (g)  carried out at 25 o C and 1 atm. Calculate  H o and  S o, then calculate  G o.

 Calculating  G o as a State Function.  Solving  G o Using Hess’s Law.  Using the following data (at 25 o C)  C diamond (s) + O 2 (g)  CO 2 (g)  G o = -397 kJ  C graphite (s) + O 2 (g)  CO 2 (g)  G o = -394 kJ  Calculate  G o for the reaction C diamond (s)  C graphite (s)

 Calculating  G o as a State Function.  Standard Free Energy of Formation (  G f o ).   G o =  n p  G f o products -  n r  G f o reactants  Methanol is a high-octane fuel used in high- performance racing engines. Calculate  G o for the reaction 2CH 3 OH(g) + 3O 2 (g)  2CO 2 (g) + 4H 2 O(g)

 A chemical engineer wants to determine the feasibility of making ethanol (C 2 H 5 OH) by reacting water with the ethylene (C 2 H 4 ) according to the equation C 2 H 4 (g) + H 2 O(l)  C 2 H 5 OH(l) Is the reaction spontaneous under standard conditions?

 The equilibrium position represents the lowest free energy value available to a particular reaction.  Free energy changes throughout the course of a reaction because it is pressure and concentration dependent.  For any 1 mole of a gas at a given temperature  S large V > S small V or S low P > S high P

 This leads to the equation  G =  G o + RT ln(Q) where Q is the reaction quotient, T is the Kelvin temperature, R is the ideal gas constant 8.31 J/mol K,  G o is the free energy at 1 atm, and  G is the free energy at a specified temperature. This derivation of the equation has been removed from the equations sheet. There is, however, another derivation that is on the sheet.

 One method for synthesizing methanol (CH 3 OH) involves reacting carbon monoxide and hydrogen gases:  CO(g) + 2H 2 (g)  CH 3 OH(l)  Calculate  G at 25 o C for this reaction where carbon monoxide gas at 5.0 atm and hydrogen gas at 3.0 atm are converted to liquid methanol.