DeltaH of Diluting 24% NaOH to 2% in H2O

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Discussion Overview

The discussion centers around the enthalpy change (DeltaH) associated with diluting a 24% sodium hydroxide (NaOH) solution to a 2% concentration in water. Participants explore the thermodynamic implications of this dilution process, including calculations of final temperature and enthalpy changes.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes that dissolving pure NaOH in water generates heat and questions the enthalpy change when diluting a 24% NaOH solution with water.
  • Another participant mentions that dilution heats are tabulated, suggesting the use of existing data for calculations.
  • A third participant provides a link to a table that illustrates how to determine the final temperature by connecting the initial and final solutions on a graph.
  • One participant challenges the correctness of the previous method and outlines an alternative procedure, questioning whether the original poster was asked to calculate the enthalpy of dilution.
  • The original poster defends their method, referencing a company’s documentation and expressing confusion over discrepancies between two curves presented in the sources.
  • Another participant argues that the original method is incomplete, asserting that the actual procedure involves three steps and three independent variables related to dilution.

Areas of Agreement / Disagreement

Participants express differing views on the correct method for calculating the enthalpy of dilution and the final temperature of the solution. There is no consensus on the appropriate approach or the validity of the methods discussed.

Contextual Notes

There are unresolved questions regarding the assumptions made in the calculations, the definitions of the variables involved, and the discrepancies noted in the referenced sources.

katchum
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Hello

I know that dissolving pure NaOH in water will generate heat. But what happens when you dilute a 24% NAOH solution with water till 2%?

Example: What is the DeltaH for 100 ml 24% NaOH solution + 50 ml H2O?

Thanks
 
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Dilution heats are tabelarized.
 
That's right.

I found this nice table: http://www.pioneercompanies.com/customers/tech/data/naoh/ENTHALPY.pdf

You just draw a line between your solutions and you can see the final temperature.
 
Last edited by a moderator:
What's wrong with my method? I was asked to calculate the final temperature of the solution.

Additionally, this is the method described by the company itself:

http://www.pioneercompanies.com/customers/tech/data/naoh/DILUTION%20OF%20SODIUM%20HYDROXIDE%20SOLUTIONS.pdf

What I don't understand is, the two curves aren't the same, or am I not seeing right? There is a flattening of the curve close to 0 % for low temperatures.

The minima aren't the same either.

(as for the enthalpy of dilution, I would substract the initial and end enthalpies with each other and that's the answer)
 
Last edited by a moderator:
Your method is two steps , the actual method consists of three steps and three independent variables for a dilution ; first composition , water , and the desired composition.
 

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