exchanged 4 marks] The molar enthalpy of vaporisation of water is 40.65 kJ mol.
ID: 703084 • Letter: E
Question
exchanged 4 marks] The molar enthalpy of vaporisation of water is 40.65 kJ mol. How much heat is required to evaporate 100 g of water from a temperature of T 298 K at an atmospheric pressure of 1 bar? Assume that the specific heat capacity of liquid 4 marks] o) Draw a schematic pressure/temperature (p/T) phase diagram of a substance, 4 marks] water is 4.184 J g K1, independent of temperature indicating the solid, liquid and gaseous regions and the characteristic points. Ice melts under pressure. Explain this observation by reference to the solid/liquid phase boundary in a sketched phase diagram of water. Hint: ice has a mass density of 0.917 g/cm3. Liquid water has a mass density of 1.000 g/cm (c) 4 marks What is the melting point of ice under a pressure of 100 bar? The enthalpy of fusion for water is 6.01 kJ mol1. Use the mass densities from part (c) in your (d) calculation [6 marks] (e) Calculate the molar entropy changes associated with the melting of ice at 1 bar and at 100 bar [2 marks] Turn overExplanation / Answer
Ans 1
Heat required to change the temperature of liquid water from 298 K to 373 K
Q1 = mass x Cp x (T2-T1)
= 100 g x 4.184 J/gK x (373-298)K
= 31380 J
Heat required to change the phase from liquid water to gas
Q2 = m x Hvap
= 100 g x 40.65 kJ/mol x 1mol/18g x 1000J/kJ
= 225833 J
Total heat required = 31380 + 225833 = 257213 J
= 257.213 kJ
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