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प्रश्न
Calculate the enthalpy change on freezing of 1.0 mol of water at 10.0°C to ice at - 10.0°C. ΔfusH = 6.03 kJ mol-1 at 0°C.
Cp[H2O(l)] = 75.3 J mol-1 K-1
Cp[H2O(s)] = 36.8 J mol-1 K-1
उत्तर
Total enthalpy change involved in the transformation is the sum of the following changes:
- Energy change involved in the transformation of 1 mol of water at 10°C to 1 mol of water at 0°C.
- Energy change involved in the transformation of 1 mol of water at 0° to 1 mol of ice at 0°C.
- Energy change involved in the transformation of 1 mol of ice at 0°C to 1 mol of ice at –10°C.
`"Total" triangle" H"= "C"_"p"["H"_2"OC"l]triangle"T" + triangle"H"_"freezing" + "C"_"p"["H"_2"O"_("s")]triangle"T"`
= (75.3 J mol-1 K-1) (0 - 10)K + (- 6.03 × 103 J mol-1) + (36.8 J mol-1 K-1) (- 10 - 0)K
= - 753 J mol-1 - 6030 J mol-1 - 368 J mol-1
= - 7151 J mol-1
= - 7.151 kJ mol-1
Hence, the enthalpy change involved in the transformation is - 7.151 kJ mol-1.
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