50.0 mL of 0.100 M aqueous solution of silver nitrate, AgNO_3 and 50.0 nL of 0.1
ID: 970061 • Letter: 5
Question
50.0 mL of 0.100 M aqueous solution of silver nitrate, AgNO_3 and 50.0 nL of 0.100 M hydrochloric acid, HC1, are mixed in a calorimeter, and the following precipitation reaction occurs: Ag^+1 (aq) + cl^-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, delta H degree , 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/degree C.Explanation / Answer
The heat produced during a reaction can be calculated using the reaction.
Qrxn = m X Cs X T
T = Change in temperature
Cs = specific hear
m = mass of the total reaction mixture
In the given problem,
T = 23.3 – 22.6 = 0.7 K
Cs = 4.18 J/g-K
m = 100 g
It was mentioned that, both the AgNO3 and HCl are assumed to be similar to water. The density of water is 1.0 g/mL and its Cs is 4.18 J/g-K. Because 50 ml of AgNO3 and 50 ml of HCl are mixed, 100ml can be considered as 100g as the density is g/mL.
Qrxn = m X Cs X T
Qrxn = 100 X 4.18 X 0.7 = 292.6 J
As the reaction is carried out in the calorimeter the heat produced in the reaction would be the enthalpy.
H = 292.6 J = 0.2926 kJ.
No. of moles of HCl in 50 ml of 0.1 M HCl = volume X molarity = 0.05 X 0.1 = 0.005 mol
The H in kJ/mol = 0.2926/0.005 = 58.52 kJ/mol
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