@X@user.full_name@X@ @GMU: Uranium -238 decays in a series of steps to Pb-206. When the material is very old, one can treat the kinetics as a decay directly to Pb and the ratio of these two can be treated as a measure of the age of a rock. A rock containing 238U and 206Pb was examined to determine its approximate age. The molar ratio of 206Pb to 238U was 0.2029. Assuming no lead was originally present and that all lead formed remained in the rock, what is the age of the rock (in years)? The half-life of 238U is 4.50e9 yr.

@X@user.full_name@X@ @GMU: Hydrogen iodide decomposes at 410°C according to second order kinetics (see reaction below). The half-life for this reaction was measured to be 6.83e3 s when the initial concentration of HI was 4.75e-3 M. What is the rate constant for this reaction?HI(g) → H2(g) + I2(g)

@X@user.full_name@X@ @GMU: What is the free energy change for the reaction below, if the reaction quotient, Q, at 25.0oC is equal to 1.43e-6?4C2H2(g) + H2(g) → C8H10(g) ΔGo = -706.560 kJ.

@X@user.full_name@X@  @GMU: What is Kp for the reaction below, if Kc = 3.28e-3 at 305.4°C?3A(s) + 2B(g) → 3C(g)

@X@user.full_name@X@ @GMU: What would the [OH-] be after addition of 5.88 mL of 0.1000 M NaOH to 25.00 mL of 0.1000 HA (a weak acid, Ka = 3.32e-5)?

@X@user.full_name@X@ @GMU: The pH of a solution of HClO4 was 4.941. What was the hydronium ion concentration?

@X@user.full_name@X@ @GMU: What is the standard free energy change for the following cell?2Cu+(aq) + Sn(s) → 2Cu(s) + Sn2+(aq) Ecoell = 0.660V

@X@user.full_name@X@ @GMU: What is the pOH of a 0.1768 M H2CO3 ? See reaction belowH2CO3 + H2O → HCO-3 + H3O+ Ka = 4.300×10-7

@X@user.full_name@X@ @GMU: What is the conjugate base and base dissociation constant of NH+4 if its acid dissociation constant is 5.600×10-10 ?

John Schreifels @GMU: What is the total entropy change at 25oC for the reaction below, if the standard entropies of reactants and products are So(C(gr)) = 5.74 J/mol*K, So (H2(g)) = 130.68 J/mol*K, and So (C7H16(g)) = 426.3000J/mol*K and the heat of formation of C7H16(g)) is -187.9000 kJ/mol.C7H16(g) → 7C(gr) + 8H2(g)