Question

free energy changed also depends on concentration. for gases, how is G related to the pressure for gases? what are standard standard pressures for gases and standard concentrations for solutes? how do you calculate ∆G for a reaction at nonstandard conditions? the equation to determine ∆G at nonstandard conditions has Q in it: what is Q? S reaction is spontaneous as long as ∆G is neg; that is, reactions always proceed as long as the products have a lower free energy than the reactants. what is so special about equilibrium? why don't reactions move away from equilibrium?

Answer 1

G= -RTln(Kp)

Kp is function of pressure of reactants and products raised to the power of their stoichiometric coefficients.

Standard condition for pressure : 1atm for gases

Standard concentration for solutes: 1 mol/ dm^{​​​​​3}​​​​dm3

This is the equation used for nonstandard conditions.

Q is the reaction quotient. It defines the direction of reaction from the very moment it is calculated and compared with equillibrium quotient Kp.

At equillibrium the total energy of the system, and surrounding becomes the minimum. Delta G becomes zero that means the Kp becomes 1. That suggests that the activity ratio of products to that of reactants has became 1 now. Means both the activities of product and reactants are equal. Even if some amount of reactant forms product after equilibrium, the formed product will come back to reactant. Which thereby means that in equilibrium the rate of forward reaction equals rate of backward reaction.