At 1 atm pressure

PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter

Problem

At 1 atm pressure, substance Q has a melting point of −12 °C and a boiling point of 54 °C. The molar enthalpy of fusion is ΔHfus=3.9 kJ mol−1\Delta H_{\text{fus}} = 3.9\,\text{kJ}\,\text{mol}^{-1}, and the molar enthalpy of vaporization is ΔHvap=27.4 kJ mol−1\Delta H_{\text{vap}} = 27.4\,\text{kJ}\,\text{mol}^{-1}. Its molar heat capacities may be assumed constant and are given below. • Cp, solid=45.0 J mol−1 °C−1C_{p,\,\text{solid}} = 45.0\,\text{J}\,\text{mol}^{-1}\,\text{°C}^{-1} • Cp, liquid=101 J mol−1 °C−1C_{p,\,\text{liquid}} = 101\,\text{J}\,\text{mol}^{-1}\,\text{°C}^{-1} • Cp, gas=68.0 J mol−1 °C−1C_{p,\,\text{gas}} = 68.0\,\text{J}\,\text{mol}^{-1}\,\text{°C}^{-1} A sample containing 1.50 mol1.50\,\text{mol} of Q is initially present as a gas at 85 °C and 1 atm. The sample is cooled until it becomes a solid at −25 °C, with the pressure remaining at 1 atm the entire time. (a) Calculate the energy released as the gas cools from 85 °C to 54 °C. (b) Calculate the energy released when the gas condenses completely at 54 °C. (c) Calculate the energy released as the resulting liquid cools from 54 °C to −12 °C. (d) Calculate the energy released when the liquid freezes completely at −12 °C. (e) Calculate the energy released as the solid cools from −12 °C to −25 °C. (f) Determine the total energy released by the sample for the entire cooling sequence.

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