MUK First Law of Thermodynamics and Change in Entropy Questions

Homework set 51. Water is vaporized reversibly at 100 °C and 1.01325 bar. The heat of vaporization is
40.69kJ mol-1.
(a) What is the value of ∆S for the water?
(b) What is the value of ∆S for the water plus the heat reservoir at 100 °C?
2. Assuming that CO2 is an ideal gas, calculate ∆ H° and ∆S° for the following process:
1CO2 (g, 298.15K,1bar) → 1CO2 (g,1000K,1bar)
Given: 𝐶̅ op = 26.648 + 42.262 x 10-3 T – 142.40 x 10-7 T2 in JK-1 mol-1
3. The temperature of an ideal monatomic gas is increased from 300 K to 500 K. What is
the change in molar entropy of the gas?
Using the first law of thermodynamics:
dq = dU + PdV
(a) if the volume is held constant
(b) if the pressure is held constant?
4. Ammonia (considered to be an ideal gas) initially at 25 °C and 1 bar pressure is
heated at constant pressure until the volume has trebled.
Given: 25.895 + 32.999×10-3T – 30.46×10-7T2 In J K-1 mol-1
Calculate
(a) q per mole
(b) w per mole
̅
(c) ∆𝐻
(e) ∆𝑆̅
5. (a) A system consists of a mole of ideal gas that undergoes the following change in
state 1X (g, 298K,10 bar) 1X (g, 298 = K,1bar)
What is the value of ∆𝑆̅ if the expansion is reversible? What is the value of ∆𝑆̅ if the
gas expands into a larger container so that the final pressure is 1 bar? (b) The same
change in state takes place, but we now consider the gas plus the heat reservoir at 298
K to be our system. What is the value of ∆𝑆̅ if the expansion is reversible? What is
the value of ∆𝑆̅ if the gas expands into a larger container so that the final pressure is 1
bar?
6. An ideal gas at 298 K expands isothermally from a pressure of 10 bar to 1 bar. What
̅, ∆𝐻
̅ and ∆𝑆̅ in the following cases?
are the values of w per mole, q per mole, ∆𝑈
(a) The expansion is reversible
(b) The expansion is free
(c) The gas and its surroundings form an isolated system, and the expansion is
reversible
(d) The gas and its surroundings for an isolated system, and the expansion is free.
In this case:
7. The purest acetic acid is often called glacial acetic acid because it is purified by
fractional freezing at its melting point of 16.6 °C. A flask containing several moles of
liquid acetic acid at 16.6 °C is lowered into an ice-water bath briefly. When it is
removed it is found that exactly 1 mol of acetic acid has frozen.
Given:
(a) What is the change in entropy of the acetic acid?
(b) What is the change in entropy of the water bath?
(c) Now consider the water bath and acetic acid are in the same system. What is
the entropy change for the combined system? Is the process reversible or
irreversible? Why?