Question

When 60.0 mL of a 0.400 M solution of HNO_{3 (aq)} is combined with 60.0 mL of a 0.400 M solution of NaOH_(aq) in a coffee-cup calorimeter, the final temperature of the solution is measured to be 26.6 ˚C. The initial temperature of the solutions is 24.0 ˚C. Calculate qrxn in joules, assuming the specific heat capacity of the final solution is 3.90 J·g–1·˚C–1, the density of the final solution is 1.04 g/mL, and the calorimeter constant is 45 J/^oC. (Hint: start with qrxn + qsoln + qcal = 0.)

The balanced chemical equation for this reaction is:

HNO_{3 (aq)} + NaOH_(aq) → H₂O_(l) + NaNO_{3 (aq)}

Answer 1

Q(rxn) = - ( Q(sol) + Q (cal))

Total volume = 60.0 + 60.0 = 120.0 ml

Mass = volume * density

= 120.0 * 1.04

= 124.8 grams

Q ( sol ) = mass * specific heat * ∆T

= 124.8 * 3.90 * ( 26.6 - 24.0 )

= 1265.472 J

Q ( cal ) = C(cal) * ∆T

= 45 * ( 26.6 - 24.0)

= 117 J

Q total = 1265.472 + 117

= 1382.472 J

Qrxn = - 1382.472 J

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