When a student mixes 50 mL of 1.0 M HCl and 50 mL of 1.0 M NaOH in a coffee-cup

Question

When a student mixes 50 mL of 1.0 M HCl and 50 mL of 1.0 M NaOH in a coffee-cup calorimeter, the temperature of the resultant solution increases from 21.0 degree C to 27.5 degree C. Calculate the enthalpy change (Delta H) for the reaction in kJ/mol HCl. (Assuming that the calorimeter loses only a negligible quantity of heat, that the total volume of the solution is 100 mL, that its density is 1.0 g/mL, and that its specific heat is 4.18 J/g middot K.) When 50.0 mL of 0.200 MAgNO_3 and 50.0 mL of 0.200 M HCl are mixed in a constant-pressure calorimeter, the temperature of the mixture increases from 23.2 degree C to 24.8 degree C. The temperature increase is caused by the following reaction: AgNO_3(aq) + HCl(aq) - rightarrow AgCl(s) + HNO_3(aq) Calculate the enthalpy change (Delta H) for this reaction in kJ/mol AgNO_3. (Assume that the combined solution has a mass of 100.0 g and a specific heat of 4.18 J/g middot degree C.)

Explanation / Answer

Q6.

Total V = 50+50 = 100 g, for D = 1 g/mL = mass = 100 g

mol = MV= 0.1*50 = 5 mmol or 5*10^-3 mol

now

Q = m*C*(Tf-Ti)

Q = 100*4.18*(27.5-21)

Q = 2717 J

for reaction

-Qrxn = Qwater

Qrxn = -2717 J

HRxn = Qrxn/n = -2717 /(5*10^-3) = -543400 J/mol = -543.400 kJ/mol

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