1. a) One mole of ice is warmed from 220 K to 330 K at a constant pressure of 1

Question

1. a) One mole of ice is warmed from 220 K to 330 K at a constant pressure of 1 bar. Find the enthalpy change for this process. b) If we assume that the volume of the ice/water does not change significantly during the process in a) what is the energy change? c) In fact, when the ice melts the density changes from 0.9167 g/cm3 to 1.000 g/cm3. If we assume that the volume change is due entirely to this density change (that is, we neglect thermal expansion of the ice/water), what is the difference between the enthalpy change and the energy change during the process? Is this a significant difference, compared to the total energy change?

Explanation / Answer

(i)energy change:

ice at 220 K is heated to water at 330K.

energy change=n cp,ice (273-220)+n (latent heat) + n cp,water (330-273)

here, n=1 mole, cp,ice=36.4 J/deg C* mol, latent heat=6.01 kJ/mol, cp,water =75.4 J mol¯1 °C¯1 =12.237 kJ

(ii)assuming that the volume does'nt change,

h=(pv)

here, p is constant and the volume doesn't change.

h1=0

if the density changes,

h=(pv)=pv=p(1/)=p(1/2 - 1/1)

p=1 bar=105 Pa

2=1.000 g/cc=1000 kg/m^3

1=0.9167 g/cc=916.7 kg/m^3

h2=-9.09 J

u-h1=12.237 kJ

u-h2=12.228 kJ

the difference between the two methods is negligible.

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