Lecture28 - Lect 28, Chem 162, Spring 2011 G = Gprod -...

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1 Lect 28, Chem 162, Spring 2011 G = G prod - G react = H - T S H and S are both relatively independent of temperature ---- hence we can use tabulated 298 K H o and S o values at temperatures different from 298 K. G, however, is never independent of temperature but is explicitly temperature dependent. G o = G o prod - G o react = H o - T S o When we calculate G o , the superscript zero, refers to standard conditions. Standard conditions means that all reactants and products are at 1.0 atm pressure or 1.00 M concentration. If not at standard conditions, we can calculate G using the formula: G = G o + RT ln Q Q = the reaction quotient, the equilibrium constant expression with the actual concentrations inserted Automatically, Q = 1 at standard conditions. If Q = 1, then ln Q = 0 and from the above formula, G = G o as expected. As reaction proceeds, Q changes until equilibrium is reached. Assume a reaction is at standard conditions and G o < 0. Then the reaction proceeds to the right. In so doing, Q will become greater than 1 (more products than reactants), and ln Q will be greater than 0. As the reaction proceeds further to the right, Q increases enough so
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2 that RT ln Q is positive enough to just cancel the negative G o . At that point G = 0 and equilibrium is reached. Assume a reaction is at standard conditions and G o > 0. Then the reaction proceeds to the left. In so doing, Q will become less than 1 (more reactants than products), and ln Q will be negative (less than 0). As the reaction proceeds further to the left, Q decreases enough so that RT ln Q is negative enough to just cancel the positive
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This note was uploaded on 11/09/2011 for the course CHEM 162 taught by Professor Siegal during the Spring '08 term at Rutgers.

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Lecture28 - Lect 28, Chem 162, Spring 2011 G = Gprod -...

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