ΔG˚ = 19.1 kJ Kb for (CH3NH2) at 25˚C is 4.4x10-4
What is the value of ΔG when [H+] = 1.6 ×10-8 M, [CH3NH3+] = 5.1x10-4, and [CH3NH2] = 0.130 M?
I got the answer as 49.1 kJ using the following equation:
ΔG= -RT ln Kb
ΔG= (-8.314 J/mol*K)(298.15 K)(ln(2.4519x10-9) = 49,146 J/mol = 49.1 kJ/mol
The answer wants it in kJ not kJ/mol. What am I doing wrong?
CH3NH2 (aq) + H2O (l) <-> CH3NH3+(aq) + OH-(aq)
we convert H+ concentration to OH-
as H+ * OH- = 10-14
OH- = 10-14 / H+ = 10-14 /1.6 ×10-8 = 0.625 * 10-6
Kb= CH3NH3+ * OH- / CH3NH2 = 5.1x10-4 mole * 0.625 * 10-6 mole / 0.130 mole = 24.5192 * 10-10 mole
G0=
-RTlnK = - 8.313 * 298.15 K * 2.303 log 24.5192 *
10-10 mole
= 8.313J/mol*K * 298.15 K * 2.303 * 8.6104 mole = 49154.366 = 49.154 KJ
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