Brian M. answered • 07/04/20

Tutor for General Chem & Organic Chem

The first step here is to determine what q(rxn) or the heat absorbed/released by the reaction is in order to determine ΔH (KJ/mol) is for AgNO3.

The question here **already** gives you the heat produced by the reaction otherwise you would have to calculate it by first determining the heat absorbed by the solution itself with equation:

q(soln) = m × C (s,soln) × ΔT

m = (0.997 g/ml)(250 mL) = 249.25 g [Multiply density of solution by total volume]

C (s,soln) = 4.18 J/g * °C the specific heat capacity of the solution

ΔT = 24.3 - 21.6 = 2.7 °C

q (soln) = 2810 J

Then since the solution **absorbed** heat that means that the reaction itself **released** heat so...

q (rxn) = - q(soln)

The heat released by the reaction is simply the **same** heat absorbed by the solution. The **negative** sign indicates the release of heat.

q (rxn) = -2810 J (convert to KJ)

q (rxn) = -2810 J × (1 kJ/1000 J) = -2.81 KJ

Use the enthalpy equation to acquire the final answer...

ΔH (rxn) = q (rxn) / mol AgNO3

Now the mols of AgNO3 in the intital reaction must be determined, this can easily be done using the formula for molarity:

M = mol (solute)/L (solution) rearrange to mol (solute) = (M)(L (solution))

mol AgNO3 = (0.220 M)(0.125 L) = 0.0275 mol AgNO3

So...

ΔH (rxn) = (-2.81 KJ) / (0.0275 mol AgNO3)

ΔH (rxn) = -102 KJ / mol AgNO3 [**Answer**]