1. (16 points) Answer the following questions related to equilibrium and chemica

Question

1. (16 points) Answer the following questions related to equilibrium and chemical potentials.

For the reaction

2NH3(g)N2(g)+3H2(g),

a mixture of nitrogen, hydrogen and ammonia gases is allowed to reach equilibrium at 400.K. When the reaction mixture is heated to 600.K, the amount of ammonia at equilibrium decreases. Why is this information sufficient to determine whether the reaction is exothermic or endothermic?

2- At 25°C, the reaction

2NO2 (g) N2O4 (g)
has an equilibrium constant of K = 8.85. A mixture of these two gases at 25°C has

PN2O4 = 0.0828 bar and PNO2 = 0.255 bar . Is this reaction mixture at equilibrium? If not, in which direction does it proceed? What is the value of rG for this reaction mixture?

c. At 25°C under standard conditions, 1 mole of trans-2-butene has 2.89 kJ/mol less Gibbs free energy than 1 mole of cis-2-butene. Yet, a pure sample of trans-2-butene is not at equilibrium; some amount of cis-2-butene has to form from it in order to give an equilibrium reaction mixture. Why is the equilibrium system a mixture rather than just a pure sample of the material with lower Gibbs free energy? Another way of asking this question: What factor causes the equilibrium mixture to have a lower Gibbs free energy than the pure trans-2-butene?

d. The sublimation temperature of CO2(s) at 1 bar is –78°C. The liquid phase of CO2(s) is not stable at 1 bar for any temperature. Using only this information, rank the values of the chemical potentials of solid, liquid, and gaseous carbon dioxide at 1 bar and –78°C and

explain your ranking.Sketch a graph ofG vs.T for these three phases at 1bar and identify the sublimation temperature on your graph. (No calculations are necessary for this question; use thermodynamic principles to determine which chemical potentials are greater than, less than, or equal to each other.)

Explanation / Answer

1)

if NH3 (the product) decrease with heat it means that adding (T) to the reaction decreases product formation, therefore K is decreased, meaning that this reaction must be exothermic. It release heat naturally so if you add more heat, then you force the equilibrium to the left; meaning the reaction is exothermic

2)

K = 8.85

K = N2O4 / (NO2)^2

solve for Q

Q = (0.0828)/(0.255^2) = 1.27

since Q is not equal to K; this is NOT in equilibrium

Q < K; therefore it means that the reaction is high in reactants, meaning the G is positive (favours reactants)

c)

The equilibrium needs to have a mixture in order to have G = 0

G = prodcts - reactants

if your products are positive in G; then you need reactants to make th eequation equal to zero

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