Use the information given below to calculate: i)delta G degree/r and ii) Kp for

Question

Use the information given below to calculate: i)delta G degree/r and ii) Kp for the following reaction at 25 degree C: Calculate tbe free energy change, delta G. for the formation of ethylene (C_2H_4) from carbon and hydrogen at 25 degree C when the partial pressures are 1.5 atm H_2 and 2.5 atm C_2H_4. then tell whether the reaction is spontaneous in the forward direction or not Consider the galv anic cell that uses the reaction C learly sketch the experimental set-up. write dow n the anode and cathode half-reactions, and give the shorthand notation for the cell.

Explanation / Answer

1) G = H - TS =) G = Hf - (Sproduct - Sreagent) =) G = 50.63 - (192 +2x130.7- 121.2)= 281.57 as G > 0 the reacction is not espontanea

2) S = -(Sproduct - Sreagent) = -213.6 + 92.9 +39.7 = -81

3) i) if the S > 0 the product are more ordered than the reagent for this reason if this S is > 0 this reacction is endotermic although H too says if the reacction is endo or exotermic the reacction

ii) -156

4) G = H - TS =) G = Hf -(Sproduct - Sreagent) rewritte G = Hf-Sproduct + Sreagent =) G = Gf + Sreagent =) Gf = G - Sreagent = Gf = -31 -192 -3x130.7 = -553.1

G = -RTLnK =) K = e-G/RT =)  K = e31/(8.31x298) = 4.08x10-4

5) 2C + 2H2 -> C2H4   Go = mHf -nS n = nproduct - nreagent and m = n C2H4 in standard conditions m = 1 and n = -3

for T = 25C RT = 25.33atml/mol PV =nRT =) think in V = 1l n = PV/RT nC2H4 = 2.5atmx1l/25.33atml/mol = 9.9x10-2mol and nH2 = 1.5atmx1l/25.33atml/mol = 5.9x10-2 mol but need the Hf of C2H4 and the entropies standard for the C and H and late replacing in the equation

6) Zn -> Zn+2 + 2e 0.76v in the cathode and Cu+2 -> Cu 0.34 in the anode for E0 = 1.1V

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