Calculating Equilibrium Constant and Making a Buffer with NH4Cl and NH3

[BThomas1219]

Homework Statement

Calculate the equilibrium constant if you are given gibbs energy for the following molecules
NH3=-26kJ/mol
H2O-237.13kJ/mol
NH4+=-79.31kJ/mol
OH-=157.3kJ/mol

How many moles of NH4Cl must be added to 1.0L of 0.10M NH3 to make a buffer whose pH is 9.0?

Homework Equations

Henderson hasselbach equation,
delta G=RTlnK

The Attempt at a Solution

1) How do you calculate equilibrium constant if you don’t have the temperature to use G=RTlnK
2) For the second half the question, I am thinking of using Henderson hasselbach equation to determine the concentration of NH4Cl. If not, how should I go about solving this question.

 

[BThomas1219]

Just need some help starting out with the problem

 

[Doobwa]

I believe unless otherwise stated, you assume T=298.15K (standard conditions).

I'm not familiar enough with buffer solutions to help with the rest, sorry!

 

[Borek]

Once you have K, Henderson-Hasselbalch is the way to go.

 

[DeeNos]

Based on the given information, the first step would be to calculate the equilibrium constant (K) using the Gibbs energy (ΔG) and the temperature (T). The equation for this would be ΔG = -RTlnK, where R is the gas constant and T is the temperature in Kelvin. Once you have calculated K, you can use the Henderson-Hasselbalch equation (pH = pKa + log [base]/[acid]) to determine the concentration of NH4Cl needed to make a buffer with a pH of 9.0.

To calculate the equilibrium constant, you will need to convert the given Gibbs energy values to standard state conditions (1 mole of substance at 1 atm pressure). Once you have K, you can use the Henderson-Hasselbalch equation to determine the concentration of NH4Cl needed. Keep in mind that the pKa value for NH4Cl is the same as the pKb value for NH3, so you can use the pKa value for NH3 in the equation.

Alternatively, you could also use the ICE table method to calculate the concentration of NH4Cl needed. This involves setting up an initial, change, and equilibrium table and using the given concentrations of NH3 and NH4Cl to solve for the unknown concentration of NH4Cl needed to achieve a pH of 9.0.

In summary, to solve this problem, you will need to calculate K using the given Gibbs energy values and temperature, and then use the Henderson-Hasselbalch equation or the ICE table method to solve for the concentration of NH4Cl needed to make a buffer with a pH of 9.0.