4 Substance X is known to exist at 1 alm in the solid, lisquid, oe vapur phase,

Question

4 Substance X is known to exist at 1 alm in the solid, lisquid, oe vapur phase, dependng os the temperature. Additiosally, the valurs of these other properties uf X have hen mdzng pcanr boing point 24.00 klml 90( You may also assyme X belaves as an ideal gis in the vapox phase Suppont a sma sample of X at 20"C is put into an evacuated flask and heated ut a constand rate unti 2 6.0 kJmol of heat has been added to the sample. Gragh the semperaturé of the sample that would be ohserved during this experiment 120 110. 100 80 2 70 50 30 40 30 20 heat added (/mol)

Explanation / Answer

Initialy the substance is in solid state.

The heat is used to increase the temperature from 20 0C to 60 0C

The change in temperature = (60 - 20)0C = 40 0C

The heat capacity of solid = 28 J / m

The heat required to reach the temperature = Moles * heat capacity * change in temperature

   = 1 * 28 * 40   

= 1120  Joules/mole =1.120 KJ/mol

The heat required for conversion of solid to liquid = Moles * enthalpy of fusion = 8 KJ / mole

Now the liquid will emit the left over energy = 0.12 KJ

The rise in temperature of liquid = heat / moles X heat capacity of liquid = 0.12 X 1000 / 1 X 28

Therefore the final temperature, = 4.280C

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