Answer to Question #159053 in Chemistry for ben

Question #159053

Determine the temperature change that occurs when 13.4 g of ammonium chloride dissolve into 2.00x10^2 g of water. The molar enthalpy of solution of ammonium chloride is 15.7 kJ/mol. Write a balanced thermochemical equation for the reaction and sketch an enthalpy diagram for this reaction.


1
Expert's answer
2021-01-29T08:22:46-0500

The balanced thermochemical equation is:

NH4Cl(s) "\\rightarrow" NH4+(aq) + Cl-(aq), ∆H = 15.7 kJ/mol.

As the enthalpy change is positive, the solution becomes colder upon the dissolution of ammonium chloride.


The number of the moles of NH4Cl is its mass, 13.4 g divided by its molar mass (53.49 g/mol):

"n = \\frac{m}{M}= \\frac{13.4}{53.49}= 0.2505" mol.


Therefore, the quantity of heat absorbed is:

"Q = -\\Delta H\u00b7n = -15.7\u00b70.2505 = -3.933" kJ.


Finally, the temperature decrease is related to the heat through the specific heat capacity of water "c = 4.18" J/ (K g):

"\u2206T = \\frac{Q}{cm} = -\\frac{3.933\u00b710^3}{4.18\u00b72.00\u00b710^2} = -4.7" K, or -4.7 °C (the temperature change in °C and in K has the same absolute value).


An enthalpy diagram for the reaction of dissolution of the NH4Cl:



In this diagram, "\u2206H_{LE}" is the lattice energy of NH4Cl.


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