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 higli 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

n = 1g / 74.55 = 0.0134 moles

m = 25 g + 1 g = 26 g

q = mC(Tf - Ti)

q = 26 * 4.184 * (24.33 - 22.12)

= 240.41 J / goC = 0.24041 kJ

delta Ho = q / n = 0.24041 / 0.0134 = 17.94 kJ / mol

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