Chemistry Exam 4

Between methanol (CH3OH) and propane (CH3CH2CH3), which has the higher boiling point and why?

(CH3OH) has a higher boiling point

For the following reaction at 25oC, Ho = +115 kJ and So = +125 J/K. Calculate Go for the reaction at 25o. SBr4(g) S(g) + 2Br2(l)

+77.8 kJ/mol

In the Haber process, ammonia is synthesized from nitrogen and hydrogen: N2 (g) + 3H2 (g) 2NH3 (g) ∆Go at 298 K for this reaction is -33.3 kJ/mol. The value of ∆G at 298 K for a reaction mixture that consists of 1.9 atm N2, 1.6 atm H2, and 0.65 atm NH3 is ________.

-1.8 kJ/mol

What is Go per mole of dichromate ions for the reduction of dichromate ions, Cr2O72-, to Cr3+ by bromide ions, Br-, in acidic solution?

-150 kJ

The equilibrium constant for the following reaction is 5.0 x 108 at 25o. What is the value for the standard change in Gibbs free energy? N2 (g) + 3H2 (g) 2NH3 (g)

-50 kJ/mol

Give the mass number for the species described. Hydrogen with no neutrons

1

Calculate the potential (in volts) for the voltaic galvanic cell indicated at 25oC (standard reduction potential for Ga3+ is -0.56V, not in book). Ga | Ga3+ (10-6 M) || Ag+ (10-4 M) | Ag

1.24 V

Which one of the following reactions is spontaneous at all temperatures? A.CO2(s) CO2(g) ΔH = +25.1 kJ B.2 NCl3(g) 3 Cl2(g) + N2(g) ΔH = -460 kJ C.2 NF2(g) N2F4(g) ΔH = -85 kJ D.none of the above

2 NCl3(g) 3 Cl2(g) + N2(g) ΔH = -460 kJ

Which one of the following has the greatest entropy? A.1 mol N2(g) at 1 atm and at 400oC. B.1 mol N2(g) at 0.5 atm and at 400oC. C.1 mol N2(g) at 0.5 atm and at 700oC. D.2 mol N2(g) at 0.5 atm and at 700oC.

2 mol N2(g) at 0.5 atm and at 700oC.2 mol N2(g) at 0.5 atm and at 700oC.

A drug used to treat hypertension undergoes a decomposition reaction to give an insoluble product. Calculate the temperature at which this reaction becomes spontaneous if the enthalpy of the reaction at 298 K is 51 kJ mol-1 and the entropy of the reaction at this temperature is 118.74 J K-1 mol-1.

430 K

Consider the standard voltaic (or galvanic) cell: Fe,Fe2+ versus Au,Au3+. Which answer identifies the cathode and gives the Eo for the cell?

Au, 1.94 V

What is the hybridization of the carbon and the second oxygen?

C = sp2, O = sp3

What is the thermochemical equation for the bond enthalpy of hydrogen? What is the energy diagram for this?

H2(g) -> 2 H(g), ΔH = +436.4 kJ/mol, endothermic energy diagram

Of the molecular elements, which has the highest boiling point? Which has the lowest boiling point?

I2 = highest; H2 = lowest

What is the thermochemical equation for the formation of ammonia (making 2 moles of ammonia) using bond enthalpies? What is the energy diagram for this?

N2(g) + 3 H2(g) -> 2 NH3(g), ΔH = -107.4 kJ/mol, exothermic energy diagram

What is the sign on the change in Gibbs free energy and the general value of K for a recharging battery?

Positive ; K<1

For a galvanic cell using Ag,Ag+ (1.0 M) and Zn,Zn2+ (1.0 M) half-cells, which of the following statements is incorrect? A.The zinc electrode is the anode. B.Electrons will flow through the external circuit from the zinc\ C.The mass of the zinc electrode will decrease as the cell operates. D.Reduction occurs at the zinc electrode as the cell operates.

Reduction occurs at the zinc electrode as the cell operates.

Consider a process for which ΔH = 211 kJ and ΔS = -57 J/K. How will raising the temperature affect ΔG for this process?

The change in Gibbs free energy will increase

Which one of the following is true? A.Entropy increases when a liquid freezes at its melting point. B.For a spontaneous process ΔG > 0. C.The number of microstates available to a system is a measure of its entropy. D.Entropy of the pure crystalline solid is zero at 0°C.

The number of microstates available to a system is a measure of its entropy.

What can be said about a chemical system that has reached a minimum in free energy?

The system has achieved equilibrium

Can the noble gases be condensed into liquids? Why or why not?

Yes - dispersion forces

Atomic number

electrons

When heat is added to a liquid, what is the resulting sign on and ?

negative; negative

How many sigma and pi bonds are there in formic acid?

sigma = 4; pi - 1

Sodium reacts violently with water according to the equation below. 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) The resulting solution has a higher temperature than the water prior to the addition of sodium. What are the signs of ∆H° and ∆S° for this reaction?

∆H° is positive and ∆S° is positive