Constant-pressure calorimeter, finding change in energy

Question

In a constant-pressure calorimeter, 50.0 mL of 0.340 M Ba(OH)2 was added to 50.0 mL of 0.680 M HCl. The reaction caused the temperature of the solution to rise from 24.07 °C to 28.70 °C. If the solution has the same density and specific heat as water, what is ΔH for this reaction (per mole of H2O produced)? Assume that the total volume is the sum of the individual volumes.

Answer 1

In this question, you are only focusing on the reaction releasing energy.

 

  Ba(OH)₂  +  2 HCl  ---->  BaCl₂  +  2 H₂O

 

We know the reaction is exothermic since the temperature of the solution increased.

To determine energy (in the form of heat) for a calorimeter (constant pressure) we can use the equation: q= m x Csp x ΔT

(1)    mass solution = mass Ba(OH)₂ + mass HCl

     mass Ba(OH)₂:  50.0 mL  x  1 g    = 50 g

                                               1mL

       mass HCl: 50.0 mL x 1 g = 50 g
                                      1mL=

     mass solution = 50 g Ba(OH)₂ + 50  HCl = 100 g

 

(2)  q = 100 g x 4.184 J/gC x (28.70° C - 24.07 °C) =1937 J

 

(3) moles H₂O  = moles HCl reacted                    (the number of moles of Ba(OH)2 is enough to exactly react with HCl                                                                          the coefficient of H2O and HCl are the same)

     50 mL x   1 L      x    0.680 mol x 2 mol _H2O  = 0.0340 moles

                 1000 mL         L              2 mole HCl

 

(4)  ΔH/mol H₂O = 1937 J /0.0340 moles H₂O = 5.70 J/mol