# chemistry questions regarding enthalpy and equilibrium

Question 1 :

The standard enthalpies of formation, at 25.00 oC, of methanol (CH4O(l)), water (H2O(l)), and carbon dioxide (CO2(g)) are, respectively, -238.7 kJ/mol, -285.8 kJ/mol, and -393.5 kJ/mol. Calculate the change in the entropy of the surroundings (in J/K) upon the combustion of 15.1 g of methanol under a constant pressure of 1.000 atm and a temperature of 25.00 oC. N.B. combustion is the reaction of this substance with molecular oxygen to produce water and carbon dioxide.

Question 2 :
At 25oC, the equilibrium constant for the reaction 2 A(aq) —-> B(aq) + C(aq) is 2.20 . If the concentration of B(aq) is 0.333 M and the concentration of C(aq) is 0.537 M, what would be the minimal concentration of A(aq) (in mol/L) required to make the reaction spontaneous?

Question 3 :
For the reaction A(aq) + B(aq) <—> C(aq) + D(aq), the equilibrium constant is 23.7 at 25oC and 35.0 at 50oC. What is the value of the standard Gibbs free energy change (in kJ) of this reaction at 75oC?

Question 4 :
We have a solution that has a concentration of 0.362 M for A(aq) and 0.650 M for B(aq). There are no other solutes initially. The reaction 2 A(aq) + B(aq) <—> 2 C(aq) + D(aq) takes place. At equilibrium, the concentration of C(aq) is 0.127 M. What is the equilibrium constant of this reaction?

Question 5 :
For the reaction 2 A(aq) <—> B(aq) + C(aq), the standard Gibbs free enthalpy change is 1.64 kJ at 25oC. The initial concentration of A(aq) is 0.555 M, the initial concentration of B(aq) is 0.301 M, and the initial concentration of C(aq) is 0.243 M. What would be the concentration of A(aq) (in mol/L) once we attain equilibrium (we are still at 25oC)?

Question 6 :
We start with a pure sample of A(g). The following equilibrium is established:

2 A(g) <—> B(g) + C(g)

The total pressure is 8.40 atm and the temperature is 25.0oC. The partial pressure of A(g) is 5.06 atm. Calculate the value of the standard Gibbs free enthalphy change (in kJ) for this reaction at 25.0oC. 