Question

1).State whether you agree or disagree with the following two statements, and explain why using thermodynamic arguments:

(a)Putting a lid on the pan of water when heating it up would enable the water to heat up more quickly(explain why using thermodynamics arguments)

(b)In mid-winter, when the temperature is less than 0 oC, ice forms from (liquid) water. This disproves the Second Law of Thermodynamics. (explain why using thermodynamics arguments)

Answer 1

1(A)The Clausius-Clapeyron equation describes the relation between pressure, temperature, and the vaporization pressure of a liquid

dlnp/dT=ΔHvap/RT2

Putting the lid on the pot will slightly raise the pressure inside the pot, therefore the boiling point will raised. The steam generated will be under somewhat higher pressure. When this happens the latent heat required to generate a pound of steam will go down. This means that you will actually generate more lbs of steam with the same amount of heat at the boiling point. But it will take more heat to raise the temperature of the water to the boiling point which offsets the lower latent heat requirement. So it would seem that you would actually generate less steam with the lid on, unless you raise the pressure and temperature extremely high, then things change drastically.

B 2nd law say that in any closed system heat will spontaneously flow from a hot region to a cold region.

If the temperature drops below freezing, the probability of water becoming ice is very high. The change from water to ice is thermodynamically irreversible. If the surrounding temperature should happen to rise above the freezing point, the probability of water becoming ice, or remaining as ice, is zero. Under these conditions the reverse change of ice to liquid water is also thermodynamically irreversible.