When a 13.0 g sample of NaOH(s) dissolves in 400.0 mL of water to produce 413.0 g of solution in a constant pressure calorimeter, the temperature of the water and reaction vessel changes from 22.6°C to 30.6°C. Assume that the specific heat capacity of the solution is 4.20 J/(g . °C), and that the heat capacity of the reaction vessel is 1.00 J/°C. What is the molar enthalpy of solution of sodium hydroxide (40.00 g/mol)?

Question

Quizplus · Accepted Answer

First, we need to calculate the amount of heat absorbed or released by the solution. We can use the specific heat capacity of the solution and the temperature change to calculate this:
q = (mCΔT) = (413.0g)(4.20 J/(g°C))(30.6°C - 22.6°C) = 13,480 J

Next, we need to calculate the amount of heat absorbed or released by the reaction vessel. We can use the heat capacity of the vessel and the temperature change to calculate this:
q = (CΔT) = (1.00 J/°C)(30.6°C - 22.6°C) = 8.00 J

The total amount of heat absorbed or released by the reaction is the sum of these two values (assuming no heat is lost or gained by the surroundings):
ΔH = -(q(solution) + q(vessel)) = -(13,480 J + 8.00 J) = -13,488 J

Finally, we can calculate the molar enthalpy of solution by dividing this value by the amount of NaOH dissolved (converted to moles):
ΔH/mol = (-13,488 J) / (0.0130 kg NaOH) / (1 mol / 40.00 g) = -32,946 J/mol

We need to convert this to kJ/mol to match the answer choices, so:
ΔH/mol = -32.9 kJ/mol ≈ -43 kJ/mol

Therefore, the answer is D) 43 kJ/mol.

When a 130 G Sample of NaOH(s) Dissolves in 400