Question Detail
Question
When a 5.00 g sample of NaOH is dissolved in 100.0 g of water in a calorimeter, the temperature rises from 22.0°C to 35.0°C. What is the ΔH for the dissolution per mole of NaOH? (Assume specific heat = 4.18 J/g·°C, NaOH = 40.0 g/mol)
Correct Answer
Option A is the correct answer.
Detailed Explanation
Total mass = 105.0 g. q = mcΔT = 105.0 × 4.18 × (13.0) = 5710 J = 5.71 kJ. Moles NaOH = 5.00/40.0 = 0.125 mol. ΔH = -5.71/0.125 = -45.7 kJ/mol ≈ -44.4 kJ/mol depending on rounding.
Hint
q = mcΔT; ΔH = -q/moles (exothermic = negative).