When a 4.348 g sample of NaOH(s) is dissolved in 100 g of water in a calorimeter

Question

When a 4.348 g sample of NaOH(s) is dissolved in 100 g of water in a calorimeter, the temperature rises from 23.6 oC to 47.4 oC. Calculate Hdiss in kJ/mol. Assume that Ccalorimeter = 35.5J/0C.

When a4 34s gsmpled n 10ralorineter. the temperature rises from 23.6 °C to 47.4 °C. Calculate Hdiss in kJ/mol. Assume that Ccalorimeter = 35 .5JOC. a. Calculate the amount of heat absorbed by the solution (soln) b. Calculate the amount of heat absorbed by the calorimeter (qcal) Determine the amount of heat given off as the 4.348g NaOH dissolved (qdiss). Look at equation 2. Make sure to include an appropriate sign indicating whether it is an endothermic () or exothermic (-) process. c. d. Determine the number of moles of NaOH that dissolved Determine the amount of heat given off per mole of NaOH dissolved (AHdiss) Look at equation 3. Provide your answer in units of kJ/mol e.

Explanation / Answer

a)

Qsoln = msoln*Cp*(Tf-Tsoln)

Qsoln = 100*4.184*(47.4-23.6) = 9957.92

b)

qcal = Ccal*dT = 35.5*(47.4-23.6) = 844.9 J

c)

heat given off

Qtotal = -(Qcal + Qsoln) = -(844.9+9957.92) = -10802.82 kJ, this is exothermic, i.e. negative 10802.82

d)

mol = mass/MW = 4.348/40 = 0.1087

e)

HRxn = Qrxn /n = -10802.82/0.1087 = -99381.96 J/mol = -99.4 kJ/mol

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