thermodynamics- what drives chemical processes?

what is a non-permissible reaction

a reaction in which the internal energy of an isolated system does not remain constant

energetically favourable reaction

• y —> x

• the free energy of y is greater than the free energy of x

• change in G<0 and disorder of the universe increases during the reaction x —> y

• this reaction occurs spontaneously

energetically unfavourable reaction

• x —> y

• if the reaction x—>y occurred change in G wild be >0and the universe would become more ordered

• this reaction may occur only if it is coupled to a second, energetically favourable reaction

how to predict a reaction

• must measure standard free-energy change

• quantity represents the gain or loss of free energy as one mole of reactant is converted to one mole of product under standard conditions

coupled reactions

• reactions can be coupled if they share one or more intermediates

• the overall free-energy change is simply the sum of the individual G values

• a reaction that is unfavourable (has a positive G value) can for this reason be driven by a second

high energy bonds

• one of the most common reactions in the cell is hydrolysis In which a covalent bond is split by adding water

• the G for this reaction is sometimes loosely termed the ‘bond energy’