A Styrofoam coffee cup serves as an inexpensive calorimeter for measurements tha

Question

A Styrofoam coffee cup serves as an inexpensive calorimeter for measurements that do not require high accuracy. To 25.0 mL of water in such a cup at 24.33^degree C a 1.00 g portion of KC1_(s)) was added. It dissolved completely after a short period of gentle stirring (using the thermometer). The minimum temperature reached was 22.12^degree C. Estimate delta H^degree for the heat of solution of KCI in kJ/mol. You may assume the solution has the same specific heat capacity as the water and the heat capacity of the cup itself and of the thermometer is negligible.

Explanation / Answer

q = ms (t2 - t1)

q = 25 x 4.184 ( 22.12 - 24.33)

q = 0.23 kJ

Number of moles of KCl = 1/74.5 = 0.013

Delta H = q / n

= 0.23/ 0.013

= 17.69 kJ / mol

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