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 $\circ$ C to 30.6 $\circ$ C. Assume that the specific heat capacity of the solution is 4.20 J/(g . $\circ$ C), and that the heat capacity of the reaction vessel is 1.00 J/ $\circ$ 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 by the solution and the reaction vessel using the equation Q = mcΔT, where Q is the heat absorbed, m is the mass, c is the specific heat capacity, and ΔT is the change in temperature.
The heat absorbed by the solution is:
Qsolution = (13.0 g)(4.20 J/(g·°C))(8.0°C) = 436.8 J
The heat absorbed by the reaction vessel is:
Qvessel = (1.00 J/°C)(8.0°C) = 8.0 J

Next, we need to calculate the amount of heat released by the dissolution of NaOH using the equation ΔH = -Qrxn/n, where ΔH is the molar enthalpy of solution, Qrxn is the heat released by the reaction, and n is the number of moles of NaOH.
The heat released by the reaction is:
Qrxn = -(436.8 J + 8.0 J) = -444.8 J
The number of moles of NaOH is:
n = 13.0 g / 40.00 g/mol = 0.325 mol

Finally, we can calculate the molar enthalpy of solution:
ΔH = -Qrxn/n = -(-444.8 J / 0.325 mol) = 1368.3 J/mol = 1.37 kJ/mol ≈ 43 kJ/mol

Therefore, the best choice is D, with a molar enthalpy of solution of 43 kJ/mol.

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

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