# When a 6.50-g sample of solid sodium hydroxide dissolve in 100.0 g

When a 6.50-g sample of solid sodium hydroxide dissolve in 100.0 g of water in a coffee-cup calorimeter, the temperature rises from 21.6 C to 37.8 C. Calculate Delta H (in kJ/mol NaOH) for the solution process

    NaOH(s) ---> Na+(aq) + OH-(aq)

Assume that the specific heat of the solution is the same as that of pure water.

• DeltaH = m C DeltaT

m = 106.5 g

C = 4.18 J/(g.K)

DeltaT = 37.8 - 21.6 = 16.2 C = 16.2 K

6.5 g NaOH = 0.1625 mol NaOH

So DeltaH = (106.5 g) . (4.18 J/(g.K)) . (16.2 K) = 7.211754 kJ

Now: 7.211754 kJ / 0.1625 mol NaOH = 44.4 (kJ/mol NaOH)

Source(s): My knowledge!