In: Chemistry
When 50.0 mL of 0.900 M Ca(NO3)2 is added to 50.0 mL of 1.80 M NaF, CaF2 precipitates, as shown in the net ionic equation below. The initial temperature of both solutions is 30.00°C. As the reaction proceeds, the temperature rises to 31.50 °C. Assuming that the reaction goes to completion, and that the resulting solution has a mass of 100.0 g and a specific heat of 4.18 J/(g ∙ °C), calculate the ΔH° for this reaction, expressed in kJ/mol Ca+2.
Ca(NO3)2(aq) + 2NaF(aq) --------------> CaF2(s) + 2NaNO3(aq)
no of moles of Ca(NO3)2 = molarity * volume in L
= 0.9*0.05 = 0.045 moles
no of moles of NaF = molarity * volume in L
= 1.8*0.05 = 0.09moles
Ca^2+(aq) + 2F^-(aq) --------------> CaF2(s)
ΔT = T2-T1
= 31.5-30 = 1.50C
m = 100g
c = 4.18J/g-0C
q = mcΔT
= 100*4.18*1.5
= 627J
no of moles of Ca^2+ = 0.045moles
ΔH° = -627J
= -627J/0.045mole = -13933J/mole = -13.933KJ/mole