F5 Chem calculation

2011-06-18 10:10 pm

In an experiment, 10 g of KCl(s) was added to 100 cm^3 of water. The mixture was then stirred until all the KCl(s) dissolved. The temperature of the mixture was found to drop by 5.5 degree Celsius. What
is the molar enthalpy change, in kJ mol^-1, of the dissolving process of
KCl(s) under the conditions of the experiment?

( Specific heat capacity of the mixture =
4.2Kg^-1K^-1; Density of water =1.0 g cm^-3; Relative atomic masses: K = 39.1, Cl = 35.5)

Ans: 18.96. Show me the steps please.

回答 (1)

andrew

2011-06-19 12:09 am

✔ 最佳答案

In an experiment, 10 g of KCl(s) was added to 100 cm³ of water. The mixture was thenstirred until all the KCl(s) dissolved. The temperature of the mixture was foundto drop by 5.5 degree Celsius. What is the molar enthalpy change, in kJmol⁻¹, of the dissolving processof KCl(s) under the conditions of the experiment?
( Specific heat capacity ofthe mixture = 4.2 kg⁻¹ K⁻¹; Density of water =1.0 gcm⁻¹; Relative atomic masses: K= 39.1, Cl = 35.5)

Note that the specific heat capacity of the mixture should be 4.2 kJ kg⁻¹ K⁻¹ or 4.2 J g⁻¹ K⁻¹.

Mass of the solution, m = 100 x 1.0 + 10 = 110 g =0.11 kg
Heat absorbed = m c ΔT = 0.11 x 4.2 x 5.5 = 2.541kJ
No. of moles of KCl used = 10/(39.1 + 35.5) = 0.134 mol
Molar enthalpy change = 2.541/0.134 = 18.96 kJ mol⁻¹

參考: andrew

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