@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 0.1807. 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: What is the rate constant at 500.54°C for the reaction below if the rate constant is 1.80e-4 s-1 at 477.00°C and the activation energy is 270.00 kJ/mol?Cyclopropane → Propene

@X@user.full_name@X@ @GMU: What would the [H3O+] be after addition of 5.94 mL of 0.1000 M NaOH to 25.00 mL of 0.1000 HA (a weak acid, Ka = 2.12e-4)?

@X@user.full_name@X@ @GMU: How much time in days would it take for a 1.5967 g sample of 18F to decay to a mass of 1.0178 g if it has a half-life of 6.588e3 s.

@X@user.full_name@X@ @GMU: What is the standard free energy change for the following cell?3Cu2+(aq) + 2Cr(s) → 3Cu(s) + 2Cr3+(aq) Ecoell = 1.080V

@X@user.full_name@X@ @GMU: What is the solubility in g/L of C2H6 at a partial pressure of 292.3 torr, if the solubility at a partial pressure of 368.8 torr is 0.02626 g/L?

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 (C9H16(g)) = 484.8200 J/mol*K and the heat of formation of C9H16(g)) is 61.8300 kJ/mol.9C(gr) + 8H2(g) → C9H16(g)

@X@user.full_name@X@ @GMU: What is the cell voltage for the following cell?2Fe3+(aq) + 3Cd(s) → 2Fe(s) + 3Cd2+(aq) ΔGo = -208.408 kJ

@X@user.full_name@X@ @GMU: NO2 at 378°C decomposes to form NO and O2 according to second order kinetics (see reaction below). The half-life for this reaction was measured to be 2.56e1 s when the initial concentration of NO2 was 9.54e-3 M. What is the rate constant for this reaction?2NO2(g) → 2NO(g) + O2(g)

@X@user.full_name@X@ @GMU: Which product in the reaction below is a base (this one first in the answer) and which product is an acid?ClO-4 + HClO → HClO4 + ClO-