How Do You Calculate ΔG for a Reaction at Non-Standard Conditions?

In summary, the standard change in Gibbs free energy (ΔG°) for the reaction 2 NO(gas) + O2(gas) <---> 2 NO2(gas) is -72.6 kJ at standard conditions of 298 K and a partial pressure of 1 bar for all species. With partial pressures of PNO = 0.500 bar, PO2 = 0.100 bar, PNO2 = 0.900 bar at 298 K, the ΔG for this reaction is -63.98 kJ. This was calculated using the equation ΔG = ΔG° + RTln(Q), where Q is the reaction quotient.
  • #1
cvc121
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Homework Statement


For a gaseous reaction, standard conditions are 298 K and a partial pressure of 1 bar for all species. For the reaction 2 NO(gas) + O2(gas) <---> 2 NO2(gas), the standard change in Gibbs free energy (ΔG°) = -72.6 kJ. What is the ΔG for this reaction at 298 K when the partial pressures are PNO = 0.500 bar, PO2 = 0.100 bar, PNO2 = 0.900 bar.

Homework Equations


Q = (PNO2)2 / (PO2)(PNO)2
ΔG = ΔG° + RTln(Q)

The Attempt at a Solution


Q = (PNO2)2 / (PO2)(PNO)2
Q = (0.900 bar)2 / (0.100)(0.500)2
Q = 32.4

ΔG = ΔG° + RTln(Q)
ΔG = -72.6 kJ + (0.008314 kJ mol- K-)(298 K)(ln 32.4)
ΔG = -72.6 + 8.6174 = -63.98 kJ

I am not sure about my approach to this question. Can anyone confirm if I am on the right track? Thanks. All help Is very much appreciated.
 
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  • #2
If you did the arithmetic correctly, this looks correct.
 

What is Gibb's Free Energy?

Gibb's Free Energy, also known as the Gibbs function or Gibbs energy, is a thermodynamic quantity that represents the maximum amount of work that can be extracted from a thermodynamic system at a constant temperature and pressure.

What is the equation for calculating Gibb's Free Energy?

The equation for calculating Gibb's Free Energy is ΔG = ΔH - TΔS, where ΔG is the change in free energy, ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.

How is Gibb's Free Energy used in thermodynamics?

Gibb's Free Energy is used to determine the spontaneity of a chemical reaction. If ΔG is negative, the reaction is spontaneous and can occur without the input of external energy. If ΔG is positive, the reaction is non-spontaneous and requires energy input to occur.

What is the relationship between Gibb's Free Energy and equilibrium?

In a closed system at constant temperature and pressure, the change in free energy is related to the equilibrium constant, K, by the equation ΔG = -RTlnK, where R is the gas constant and T is the temperature in Kelvin. This means that the lower the value of ΔG, the more favorable the reaction is at reaching equilibrium.

What factors affect Gibb's Free Energy?

The factors that affect Gibb's Free Energy include temperature, pressure, and the concentrations of reactants and products. Changes in these factors can influence the spontaneity and equilibrium of a reaction, and ultimately affect the value of ΔG.

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