Calculating Heat of Formation for NH4Cl Using Calorimetry

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Discussion Overview

The discussion revolves around calculating the heat of formation for ammonium chloride (NH4Cl) using calorimetry data obtained from a lab experiment. Participants are exploring the reactions involved, the necessary calculations for enthalpy change (deltaH), and the implications of heat capacities in their calculations.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant describes the calorimetry experiment involving 50ml of 1.51M NH3 and 50ml of 1.59M HCl, resulting in a temperature change (deltaT) of 8.6°C.
  • Another participant requests the original poster to provide their attempt at solving for deltaH and suggests writing out the reactions involved.
  • The original poster identifies the reactions as NH3(aq) + HCl(aq) = NH4Cl(aq) and NH4Cl(s) = NH4Cl(aq), but seeks further guidance on the next steps.
  • A participant clarifies the dissociation of NH3 and HCl in water, proposing that NH4+(aq) + Cl-(aq) leads to NH4Cl(aq) and prompts the original poster to determine the other reaction.
  • There is a discussion about the need for the heat capacity of the ammonium chloride solution and the potential assumption of using the heat capacity of pure water, with a note on the inaccuracy of this assumption.

Areas of Agreement / Disagreement

Participants are collaboratively working through the problem, but there is no consensus on the calculations or the specific next steps to take. Multiple viewpoints on the reactions and assumptions regarding heat capacities are present.

Contextual Notes

There are unresolved aspects regarding the heat capacity of the ammonium chloride solution and the implications of using the heat capacity of pure water. The exact concentration of the resulting solution is also not determined, which may affect the calculations.

Who May Find This Useful

This discussion may be useful for students and educators involved in chemistry or thermodynamics, particularly those interested in calorimetry and reaction enthalpy calculations.

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Homework Statement


i did a lab calorimeter lab with 50ml 1.51M nh3 and 50ml 1.59M hcl yeilding nh4cl (aq)
the deltaT was 8.6 degC
second part is 100ml of h2o and 4.082g nh4cl
deltaT was -2.8 degC

Homework Equations


how do i find deltaH per mole for each reaction?

The Attempt at a Solution

 
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Give us your try at the answer...

Hint: Write out the reactions for the first part and the second part. What form was the ammonia? Was it aqueous? How should that be written?
 
its nh3(aq) + hclz(aq) = nh4cl(aq)
and nh4cl(s) = nh4cl(aq)

but where do i go from there?
 
NH3 in water is NH4+ OH-
HCl in water is H3O+ Cl-

one of the two reactions is:

NH4+(aq) + Cl-(aq) ----> NH4Cl(aq)

Can you determine the other reaction?

You will need the heat capacity of the ammonium chloride solution. Can you determine what the concentration will be?
Alternatively, you could assume the heat capacity of pure water, but it won't be an exact solution. Can you think of why you need to obtain the heat capacity?
 

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