A 19.2g quantity of dry ice (solid carbon dioxide) is allowed to sublime (evaporate) in an apparatus. Calculate the expansion work done against a constant external pressure of 0.995 atm and at a constant temperature of 22 degrees C. Assume that the initial volume of dry ice is negligible and that CO2 behaves like an ideal gas.

Answer : The expansion work done against a constant external pressure is, -1063.65 J

Explanation :

First we have to calculate the moles of dry ice .

Given:

Molar mass of = 44 g/mole

Mass of = 19.2 g

Now put all the given values in the above expression, we get:

Now we have to calculate the volume of dry ice.

Using ideal gas equation:

where,

P = Pressure of gas = 0.995 atm

V = Volume of gas = ?

n = number of moles  = 0.436 mole

R = Gas constant =

T = Temperature of gas =

Putting values in above equation, we get:

As initially, volume of dry ice is negligible. So,

Volume expanded = Volume of dry ice

Thus,

Expansion work = -(Pressure × Volume)

Expansion work = -0.995 atm × 10.6 L

Expansion work = -10.5 L.atm

Conversion used : (1 L.atm = 101.3 J)

Expansion work = -10.5 × 101.3 = -1063.65 J

Therefore, the expansion work done against a constant external pressure is, -1063.65 J

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