Question

The standard Gibbs energy of reaction, ÄG°, for the dissociation of phenol is 56.4 kJ mol-1 at 298 K. Calculate the pKa of phenol.

a.
9.88
c.
4.12
b.
22.8
d.
5.24​

Answer 1

The pKa of phenol can be calculated using the standard Gibbs energy of reaction. The pKa is approximately 9.88.

Step-by-step explanation:

The pKa of phenol can be calculated using the standard Gibbs energy of reaction, ÄG°. The equation relating pKa to ÄG° is:

pKa = -log(Ka)

where Ka is the acid dissociation constant. To calculate the pKa, we need to convert ÄG° from kJ/mol to J/mol:

ÄG° = 56.4 kJ/mol = 56400 J/mol

Then, we can use the equation:

pKa = -log(Ka) = -log(e^(-ÄG°/RT))

Substituting the given values:

pKa = -log(e^(-56400 J/mol / (8.314 J/mol·K × 298 K)))

pKa ≈ 9.88