Given that the normal boiling point of CCl4 is 77 °C, which of the following statements about the process below is/are correct? You may choose more than one, or none, of the statements.
CCl4(l, 68 °C, 1 atm) ⟶ CCl4(g, 101 °C, 1 atm)
Assume that the temperature of the surroundings is constant and also equal to 101 °C.
Note: The normal boiling point (Tnbp) is the boiling temperature at 1 atm. The phase change is reversible at the normal boiling point but irreversible if P = 1 atm and T ≠ Tnbp.
a. The entropy of the system increases: ΔS > 0.
b. The entropy of the surroundings increases: ΔSsurr > 0.
c. The entropy of the universe increases: ΔSuniv > 0.
d. Work is done by the system on the surroundings.
e. Heat flows from the system into the surroundings.
f. The entropy change for the system is equal to ΔH / Tvap.
g. The entropy change for the system is equal to ΔH / Tsurr.
h. The process is thermodynamically reversible.
To determine which of the statements are correct, we need to analyze the given process and consider the principles of thermodynamics.
1. The entropy of the system increases: ΔS > 0 (Statement a).
- This statement is correct. The change in entropy of the system is positive because the substance transitions from the liquid phase to the gas phase, which leads to an increase in disorder or randomness.
2. The entropy of the surroundings increases: ΔSsurr > 0 (Statement b).
- This statement is correct. When a substance boils and converts from liquid to gas, heat is absorbed from the surroundings. This heat transfer increases the randomness of the surroundings, resulting in an increase in entropy.
3. The entropy of the universe increases: ΔSuniv > 0 (Statement c).
- This statement is correct. The total change in entropy of the system and surroundings combined is always positive for a process that occurs irreversibly under constant temperature and pressure conditions.
4. Work is done by the system on the surroundings (Statement d).
- This statement is incorrect. In this process, the substance is vaporizing, and no work is being done on the surroundings by the system. Work would occur if, for example, the substance expanded against a piston.
5. Heat flows from the system into the surroundings (Statement e).
- This statement is correct. During the process of vaporization, energy in the form of heat flows from the surroundings into the system, causing the liquid to vaporize.
6. The entropy change for the system is equal to ΔH / Tvap (Statement f).
- This statement is incorrect. The entropy change for the system during a phase change at constant temperature and pressure is ΔH / T, where ΔH is the enthalpy change (heat absorbed or released) and T is the temperature at which the phase change occurs. In this case, it would be ΔH / 101 °C, not ΔH / Tvap.
7. The entropy change for the system is equal to ΔH / Tsurr (Statement g).
- This statement is also incorrect. Similar to the above explanation, the entropy change for the system during the phase change is not ΔH / Tsurr. It would be ΔH / 68 °C, the initial temperature of the liquid.
8. The process is thermodynamically reversible (Statement h).
- This statement is incorrect. The given process occurs irreversibly since the temperature at which the substance is boiling (101 °C) is not its normal boiling point (77 °C). Irreversible processes have higher entropy changes compared to reversible processes.
Correct Statements: a. The entropy of the system increases: ΔS > 0.
b. The entropy of the surroundings increases: ΔSsurr > 0.
c. The entropy of the universe increases: ΔSuniv > 0.
Incorrect Statements: d. Work is done by the system on the surroundings.
f. The entropy change for the system is equal to ΔH / Tvap.
g. The entropy change for the system is equal to ΔH / Tsurr.
h. The process is thermodynamically reversible.