The ΔH for the solution process when solid sodium hydroxide dissolves in water is 44.4 kJ/mol. When a 12.6-g sample of NaOH dissolves in 250.0 g of water in a coffee-cup calorimeter, the temperature increases from 23.0 °C to ________°C. Assume that the solution has the same specific heat as liquid water, i.e., 4.18 J/g-K.
A)35.2
B)24.0
C)36.4
D)35.7
E)40.2

Question

Quizplus · Accepted Answer

The heat absorbed by the solution can be calculated using q = m × c × ΔT. First, convert 12.6 g of NaOH to moles (12.6 g / 40.0 g/mol = 0.315 mol). The heat released is 0.315 mol × 44.4 kJ/mol = 13.986 kJ = 13986 J. The total mass of the solution is 12.6 g + 250.0 g = 262.6 g. Using q = m × c × ΔT, we have 13986 J = 262.6 g × 4.18 J/g-K × ΔT. Solving for ΔT gives ΔT = 12.7°C. The final temperature is 23.0°C + 12.7°C = 35.7°C.

The ΔH for the Solution Process When Solid Sodium Hydroxide