The third law of thermodynamics demonstrates: a) entropy is a function of pressu

Question

The third law of thermodynamics demonstrates: a) entropy is a function of pressure b) an engine could be 100% efficient if it were operated at OK c) the entropy of the universe is always increasing d) absolute entropy values may be measured 1.6 g CH_4 is mixed with 2.2 g C0_2. The mole fraction of CO_2 is: a) 1.375 b) 0.579 c) 0.500 d) 0.333 The formula Delta S = C_p In T_2/T_1 is valid when: a) the temperature is constant b) the pressure vs constant c) the volume is constant d) system is adiabatic A 1.0 L container contains a 100 cm^3 piece of Al, the rest, air. The pressure is increased from 1.00 atm to 10.00 atm. Assume the air behaves as an ideal gas. Calculate Delta G for this process.

Explanation / Answer

third law of thermodynamics states that entropy of a perfect crystal approaches zero value as the temperature reaches absolute 0 value which is -273 K

At absolute temperature, all the motions exhibited by the atoms (vibrational, rotational etc) are stopped. That means the structure of matter is in perfect order. And as we know entropy is measure of disorder, but when the structure is in perfect order, entropy becomes 0.

Therefore the correct option is d - Absolute entropy values may be measured

#4

We have 1.6 g CH4 and 2.2 g CO2

We will first find moles of each substance

Mol = mass in g / Molar mass

mol of CH4 = 1.6 g/16 g mol^-1 = 0.1

mol of CO2 = 2.2 g/ 44 g.mol&-1 = 0.05

mol fraction is calculated as

Mole fraction = mol of a substance/ total moles

Mole fraction of CO2 = mol of CO2 / ( mol CO2 + mol CH4)

= 0.05/ ( 0.05 + 0.1)

= 0.05/0.15

= 0.333

Option d is the correct choice

#5

The term Cp is known as specific heat at constant pressure

Therefore the formula delta S = Cp ln (T2/T1) must be valid when pressure is constant.

Therefore the correct choice is option b

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