Chemistry: Gibbs Free Energy
Put the following in the correct location: A. ΔG > 0 B. ΔG < 0 - spontaneous - nonspontaneous - exergonic - endergonic
A. ΔG > 0 - nonspontaneous - endergonic - products are found higher than reactants on diagram B. ΔG < 0 - spontaneous - exergonic - products are found lower than reactants on diagram
Effects of ΔH, ΔS, and T on Spontaneity ΔH ΔS Outcome + + Spontaneous at high T + - Nonspontaneous at all T - + Spontaneous at all T - - Spontaneous at low T
Effects of ΔH, ΔS, and T on Spontaneity ΔH ΔS Outcome + + Spontaneous at high T + - Nonspontaneous at all T - + Spontaneous at all T - - Spontaneous at low T
Equation: Gibbs Free Energy ΔG = ΔH - TΔS ΔG = change in Gibbs free energy ΔH = change in enthalpy TΔS = (T = temperature in Kelvins) represents the total amount of energy that is absorbed by a system when its entropy increases reversibly The change in Gibbs free energy is a measure of the change in the enthalpy and the change in entropy as a system undergoes a process, and it indicates whether a reaction is spontaneous or nonspontaneous.
Equation: Gibbs Free Energy ΔG = ΔH - TΔS ΔG = change in Gibbs free energy ΔH = change in enthalpy TΔS = (T = temperature in Kelvins) represents the total amount of energy that is absorbed by a system when its entropy increases reversibly The change in Gibbs free energy is a measure of the change in the enthalpy and the change in entropy as a system undergoes a process, and it indicates whether a reaction is spontaneous or nonspontaneous.
Equation: Gibbs Free Energy from Reaction Quotient - To determine the free energy change for a reaction that is in progress (because the standard state conditions of 1 M no longer apply) ΔGrxn = ΔG°rxn + RT ln Q = RT ln Q/Keq ΔG°rxn = standard free energy change for a reaction R = ideal gas constant (8.314) T = temperature in Kelvins Keq = equilibrium constant Q = reaction quotient If the ratio of Q/Keq is less than one (Q < Keq), then the natural log will be negative, and the free energy change will be negative, so the reaction will spontaneously proceed forward until equilibrium is reached. If the ration of Q/Keq is greater than one (Q > Keq), then the natural log will be positive, and the free energy change will be positive. In this case, the reaction will spontaneously move in the reverse direction until equilibrium is reached. If the ratio is equal to one, the reaction quotient is equal to the equilibrium constant; the reaction is at equilibrium, and the free energy change is zero (ln 1 = 0).
Equation: Gibbs Free Energy from Reaction Quotient - To determine the free energy change for a reaction that is in progress (because the standard state conditions of 1 M no longer apply) ΔGrxn = ΔG°rxn + RT ln Q = RT ln Q/Keq ΔG°rxn = standard free energy change for a reaction R = ideal gas constant (8.314) T = temperature in Kelvins Keq = equilibrium constant Q = reaction quotient If the ratio of Q/Keq is less than one (Q < Keq), then the natural log will be negative, and the free energy change will be negative, so the reaction will spontaneously proceed forward until equilibrium is reached. If the ration of Q/Keq is greater than one (Q > Keq), then the natural log will be positive, and the free energy change will be positive. In this case, the reaction will spontaneously move in the reverse direction until equilibrium is reached. If the ratio is equal to one, the reaction quotient is equal to the equilibrium constant; the reaction is at equilibrium, and the free energy change is zero (ln 1 = 0).
Equation: Standard Gibbs Free Energy from Equilibrium Constant ΔG°rxn = -RT ln Keq ΔG°rxn = standard free energy change for a reaction R = ideal gas constant (8.314) T = temperature in Kelvins Keq = equilibirum constant - the greater the value of Keq, the more positive the value of its natural logarithm - the more positive the natural logarithm, the more negative the standard free energy change, which means the more spontaneous the reaction
Equation: Standard Gibbs Free Energy from Equilibrium Constant ΔG°rxn = -RT ln Keq ΔG°rxn = standard free energy change for a reaction R = ideal gas constant (8.314) T = temperature in Kelvins Keq = equilibirum constant - the greater the value of Keq, the more positive the value of its natural logarithm - the more positive the natural logarithm, the more negative the standard free energy change, which means the more spontaneous the reaction
Equation: Standard Gibbs Free Energy of Reaction The free energy change of reactions can be measured under standard state conditions to yield the standard free energy. For standard free energy determinations, the concentrations of any solutions in the reaction are 1 M. The standard free energy of formation, ΔG°f, for any element under standard state conditions is, by definition, zero. ΔG°rxn = ΣΔG°f,products - ΣΔG°f,reactants ΔG°rxn = free energy change that occurs when a reaction is carried out under standard state conditions (298 K and 1 atm) ΣΔG°f,products = sum of the standard free energies of the products ΣΔG°f,reactants = sum of the standard free energies of the reactants
Equation: Standard Gibbs Free Energy of Reaction The free energy change of reactions can be measured under standard state conditions to yield the standard free energy. For standard free energy determinations, the concentrations of any solutions in the reaction are 1 M. The standard free energy of formation, ΔG°f, for any element under standard state conditions is, by definition, zero. ΔG°rxn = ΣΔG°f,products - ΣΔG°f,reactants ΔG°rxn = free energy change that occurs when a reaction is carried out under standard state conditions (298 K and 1 atm) ΣΔG°f,products = sum of the standard free energies of the products ΣΔG°f,reactants = sum of the standard free energies of the reactants
True or False: Exothermic reactions release energy and are spontaneous (ΔG < 0), whereas, endothermic reactions absorb energy and are nonspontaneous (ΔG > 0).
False. Exergonic reactions release energy and are spontaneous (ΔG < 0), whereas, endergonic reactions absorb energy and are nonspontaneous (ΔG > 0). *Be careful not to confuse endergonic/exergonic (describing Gibbs free energy) with endothermic/exothermic (describing enthalpy).
True or False: The rate of the reaction depends on ΔG.
False: The rate of the reaction depends on the activation energy, Ea, not ΔG. Spontaneous reactions may be fast or slow. The rate of a reaction relates to the kinetics of the reaction, which involves Ea. Whereas, the spontaneity (and stability) of a reaction relates to the thermodynamics of a reaction, which involves ΔG.
Gibbs Free Energy
Gibbs Free Energy
True or False: Boiling is an endothermic process.
True. Boiling is an endothermic process. When water boils, hydrogen bonds are broken (absorbs energy) and ΔH is positive.
True or False: If ΔG is negative, the reaction is spontaneous. If ΔG is positive, the reaction is nonspontaneous.
True. If ΔG is negative, the reaction is spontaneous. If ΔG is positive, the reaction is nonspontaneous. If ΔG is zero, the system is in a state of equilibirum; ΔH = TΔS. - Once at the energy minimum state --- equilibrium --- the system will resist any changes to its state, and the change in free energy is zero.
True or False: The change in Gibbs free energy for each phase change in equilibrium is zero.
True. The change in Gibbs free energy for each phase change in equilibrium is zero, as is the case for all equilibria. If ΔG is zero, the system is in a state of equilibirum; ΔH = TΔS. - Once at the energy minimum state --- equilibrium --- the system will resist any changes to its state, and the change in free energy is zero.