4.07 – Free Energy & Equilibrium

We have seen how free energy is related to enthalpy and entropy.  Now we will look at how it can be connected to equilibrium terms, K and Q.

Lesson Objectives

  • Calculate ΔG under nonstandard conditions. (19.7)
  • Relate ΔG° and the equilibrium constant. (19.7)

You should begin this mission by reviewing the key ideas presented in the slides below.  These slides refer to section 19.7 of the text.

Now that you've seen these ideas, it's time to practice the calculations.  Work through the practice problems that follow the samples in the slides below.

When you are finished working these problems out, post your notes and text practice to OneNote.

Now that you have a handle on this material, work through these mastery problems.  You can check your answers on OneNote.  Make sure to post your stamped work on OneNote after you are finished.

19.76  Consider the reaction 6 H2(g) + P4(g) → 4 PH3(g).

(a) Using data from Appendix C, calculate ΔG° at 298 K.

(b) Calculate ΔG at 298 K if the reaction mixture consists of 8.0 atm of H2, 0.050 atm of P4, and 0.22 atm of PH3.


19.78  Write the equilibrium constant expression and calculate the value of the equilibrium constant for each of the following reactions at 298 K, using data from Appendix C.

(a) NaHCO3(s) ⇆ NaOH(s) + CO2(g)

(b) 2 HBr(g) + Cl2(g) ⇆ 2 HCl(g) + Br2(g)

(c) 2 SO2(g) + O2(g) ⇆ 2 SO3(g)

 19.82  The Kb for methylamine (CH3NH2) at 25°C is given in Appendix D.

(a) Write the chemical equation for the equilibrium that corresponds to Kb.

(b) By using the value of Kb, calculate ΔG° for the equilibrium in part (a).

(c) What is the value of ΔG at equilibrium?

(d) What is the value of ΔG when [H+] = 1.5 × 10–8 M, [CH3NH3+] = 5.5 × 10–4 M, and [CH3NH2] = 0.120 M?

19.95  Cells use the hydrolysis of adenosine triphosphate (ATP) as a source of energy. The conversion of ATP to ADP has a standard free-energy change of −30.5 kJ/mol. If all the free energy from the metabolism of glucose,

C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(l)

goes into the conversion of ADP to ATP, how many moles of ATP can be produced for each mole of glucose?

2001 FRQ #2

It appears you've figured out equilibrium from all angles.  Well done Visitor!