Question

6.8

The addition of hydrochloric acid to a silver nitrate solution precipitates silver chloride according to the reaction:

AgNO3(aq)+HCl(aq)?AgCl(s)+HNO3(aq)

When 50.0 mL of 0.100 M  AgNO3 is combined with 50.0 mL of 0.100 M HCl in a coffee-cup calorimeter, the temperature changes from 23.40 ?C to 24.21 ?C.

Part A

Calculate ?Hrxn for the reaction as written. Use 1.00 g/mL as the density of the solution and Cs=4.18J/(g??C) as the specific heat capacity of the solution.

Express the energy to two significant figures and include the appropriate units.

?Hrxn =

Answer 1

Sol:-

Number of moles of AgNO₃ = 0.100 M x 0.050 L = 0.005 mol  

Number of moles of HCl = 0.100 M x 0.050 L = 0.005 mol

Given reaction is :

AgNO₃(aq) + HCl (aq) ----------> AgCl (s) + HNO₃ (aq)

I 0.005 mol 0.005 mol 0 0

C -0.005 - 0.005 + 0.005 0.005

F 0.00 mol 0.00 mol 0.005 mol 0.005 mol

Hence 0.005 mol of AgCl are formed

Total volume of the solution = 50.0 mL + 50.0 mL = 100.0 mL

therefore

Mass of the solution ( m) = density of the solution x volume of the solution

Mass of the solution ( m) = 1.00 g/mL x 100.0 mL = 100 g

also we know that

q = m.C .delta T

q = (100g) (4.184 J/g ⁰C ) ( 24.21 - 23.40 )⁰C

q = 338.304 J

q = 0.339 KJ

Now

delta H = - q / n

delta H = - 0.339 KJ / 0.005 mol

delta H = - 67.8 KJ/mol

Hence delta H = - 68 KJ/mol