Question

A calorimeter contains 35.0 mL of water at 15.0 ∘C . When 1.70 g of X (a substance with a molar mass of 76.0 g/mol ) is added, it dissolves via the reaction

X(s)+H2O(l)→X(aq) and the temperature of the solution increases to 25.0 ∘C .

Calculate the enthalpy change, ΔH, for this reaction per mole of X.

Assume that the specific heat of the resulting solution is equal to that of water [4.18 J/(g⋅∘C)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings. Express the change in enthalpy in kilojoules per mole to three significant figures.

Answer 1

mass of water = volume * density

= 35*1.00

= 35 grams

mass of solution = mass of water + mass of X

= 35 + 1.70

= 36.70 grams

heat = mass of solution * specific heat of solution * delta T

= 36.70 * 4.18 * (25 - 15)

= 1534.06 Joules

now moles of X = mass / molar mass

= 1.70 / 76

= 0.02237

now,

0.02237 moles produces = 1534.06 joules

1 mole will produce = 1534.06 / 0.02237

= 68576.66 joules/mol

or 68.576 KJ/mol or 68.6 KJ/mol

any query please comment

if satisfied please rate it thanks