Question

The dissolution of NH4ClO4(s) in water is endothermic, with ΔHsoln = +33.5kJ/mol.

If you prepare a 1.00 m solution of NH4ClO4 beginning with water at 29.5 ∘C, what is the final temperature of the solution (in ∘C)? Assume that the specific heats of both pure H2O and the solution are the same, 4.18 J/(K⋅g).

Express the temperature in degrees Celsius to three significant digits.

Answer 1

1.00 m solution means 1000 g of water dissolves 1 mole of NH4ClO4.The dissolution absorbs 33.5 kJ = 33.5×1000 J of heat.

Mass of 1.00 mole of NH4ClO4 is = moles × molar mass = 1 mole × 117.49 g/mole = 117.49 g

Total mass of solution = 1000 g × 117.49 g = 1117.49 g

Heat taken by solution = mass of solution × specific heat capacity × (Final temperature - Initial temperature )

Or; 33.5 × 1000 = 1117.49×4.18×(Final temperature - 29.5)

Final temperature = 97.7 ⁰ C