Calculating Equilibrium Constant and Making a Buffer with NH4Cl and NH3

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Discussion Overview

The discussion revolves around calculating the equilibrium constant using Gibbs energy values and determining the amount of NH4Cl needed to create a buffer solution with a specific pH using NH3. The scope includes theoretical calculations and application of the Henderson-Hasselbalch equation.

Discussion Character

  • Homework-related, Mathematical reasoning

Main Points Raised

  • One participant questions how to calculate the equilibrium constant without a specified temperature, suggesting the use of the equation G=RTlnK.
  • Another participant proposes using the Henderson-Hasselbalch equation to find the concentration of NH4Cl needed for the buffer solution.
  • A third participant suggests assuming standard conditions (T=298.15K) unless stated otherwise for the equilibrium constant calculation.
  • One participant confirms that once the equilibrium constant (K) is determined, the Henderson-Hasselbalch equation is the appropriate method to proceed with the buffer calculation.

Areas of Agreement / Disagreement

Participants generally agree on the use of the Henderson-Hasselbalch equation for the buffer calculation, but there is uncertainty regarding the temperature assumption for calculating the equilibrium constant.

Contextual Notes

There is a lack of clarity on the temperature to be used for the Gibbs energy calculations, which may affect the determination of the equilibrium constant.

BThomas1219
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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.
 
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Just need some help starting out with the problem
 
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!
 
Once you have K, Henderson-Hasselbalch is the way to go.
 

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