Part 1: A common chemistry demonstration is to dissolve ammonium nitrate into wa

Question

Part 1:

A common chemistry demonstration is to dissolve ammonium nitrate into water. In a particular demonstration, 5.81 grams of ammonium nitrate were dissolved in 100.00 mL of water. As a result, the temperature of the solution dropped from 25.0 oC to 20.8 oC. Calculate q of the solution in Joules (assume m to be the total mass of solution).

Part 2:

How many moles of ammonium nitrate were dissolved in the solution?

Part 3:

Which of the following represents the sign of Hsoln of ammonium nitrate. In other words, which represents the sign of H for the below process:

NH4NO3(s) NH4(aq) + NO3(aq)

Part 4

Calculate the Hsoln of ammonium nitrate. In other words, calculate H (in kJ/mol) for the below process:

NH4NO3(s) NH4(aq) + NO3(aq)

Explanation / Answer

part 1)

heat = m * s * deltaT

= ( 100 ml x 1.0 g/ml ) * 4.184 J/g-oC * ( 25.0 - 20.8 ) oC

= 1757.28 J

this heat is released.

part 2)

moles of ammnoium nitrate = mass / molar mass

= 5.81 g / 80.043 g/mol

= 0.073 mol

part 3) NH4NO3(s) NH4(aq) + NO3(aq)   H = - ve

part 4)

Hsol = q / moles of ammonium nitrate

= - 1757.28 J / 0.073 mol

= - 24209.6 J/mol

= - 24.2 kJ/mol

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