Which of the following quantities an element has a value of zero in the standard

Question

Which of the following quantities an element has a value of zero in the standard state? A. I only B. II only C. III only D. I land II E. I, ll, and II For the reaction: CO(g) + 2 H_2(g) rightarrow CH_3OH(g) K_p = 91.4 at 350 K and K_p = 2.05 times 10^4 at 298 K. What is the value of Delta H degree? A. 49.9 kJ/mol B. 2.08 times 10^3 kJ/mol C. 3.74 times 10^-2 kJ/mol D. 217 kJ/mol E. 446 kJ/mol In a zinc-lead cell the reaction is: Pb^2+(aq) + Zn_(s) rightarrow Pb_(s) + Z_n^2+(aq) E^+ = +0.637 V Which of the following statements about this cell is FALSE? A. The zinc electrode is the cathode. B. The reaction will go in the direction indicated. C. The shorthand notation is Zn(s)|Zn^2+(aq.10m)||Pb^2+ (aq 1.0M)|Pb(s) D. The actual cell voltage is less than +0.637 volts because of concentration polarization and possible other factors. E. The lead electrode is the cathode. Predict the species that will be reduced first the following mixture of molten salts undergoes electrolysis. FeBr_3(l) Znl_2(l) MgBr_2(l) A. Zn^2+ B. Mg^2+ C. Br^- D. Fe^3+ E. I^- Determine E degree cell for the reaction: 2 Ag^+ + Mg rightarrow 2 Ag + Mg^2+. The half reactions are: Mg^2+ (aq) + 2 e^rightarrow Mg(s) E degree = -2.356 V Ag^+(aq) + e^rightarrow Ag(s) E degree = 0.800 V A. + 0.756 V B. -0.756 V C. +3.156 V D. -1.556 V E. +1.556 V Determine K_eq at 25 degree C for the following reaction: Pb^2+ (aq) cu(s) Cu2 (aq)+Pb(s) The half reactions are: Pb^2+(aq) 2 e^Pb(s) E degree = -0.125 V Cu^2+(aq) + 2 e^- Cu(s) E degree = +0.337 V A. 2 times 10^69 B. 2 times 10^-15 C. 2 times 10^-16 D. 2 times 10^8 E. 6 times 10^-4

Explanation / Answer

Ans 14 . D . I and II only

Enthalpy change and gibbs free energy change of formation of any element in standard state is 0 because enthalpy of formation of pure element when it is already in its standard state , no energy is absorbed or released . Hence gibbs free energy change associated with the particular element in its standard state is also 0

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