50.0 mL of 0.100 M aqueous solution of silver nitrate, AgNO_3, and 50.0 ML of 0.

Question

50.0 mL of 0.100 M aqueous solution of silver nitrate, AgNO_3, and 50.0 ML of 0.100 M hydrochloric acid, HCl, are mixed in a calorimeter, and the following precipitation reaction occurs: Ag^+1 (aq) + c1^-1 (aq) rightarrow AgCl (s) If the two solutions were initially at 22.6 degreeC, and the final temperature is 23.3 degreec, calculate the enthalpy change, DeltaHdegree, in kJ/mole for this reaction. Assume that the reaction proceeds to completion, both aqueous solutions have the properties of water, and that the calorimeter constant is 25 J/degreeC.

Explanation / Answer

volume of solution/water = 50 mL + 50 mL = 100 mL
density of water = 1 g/mL
mass of water = volume* density = 100 g

specific heat capacity,
c of water = 4.186 JgoC

delta T = 23.3-22.6 = 0.7 oC

use:
Q =( C+m*c)*delta T
= (25 + 100*4.186)*0.7
= 310.52 J

moles of Ag+ reacted = 50 mL * 0.1 M = 5 mmol
moles of Cl- reacted = 50 mL * 0.1 M = 5 mmol

5 mmol = 0.005 mol releases 310.52 J

DELTA H0 = 310.52 J/0.005 mol
=62104 J/mol
=62.1 KJ/mol

Answer: 62.1 KJ/mol

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