Skip to main content
Pearson+ LogoPearson+ Logo
Ch.19 - Chemical Thermodynamics
All textbooksBrown 14th EditionCh.19 - Chemical ThermodynamicsProblem 23b
Chapter 19, Problem 23b

The normal boiling point of Br2(𝑙) is 58.8  °C, and its molar enthalpy of vaporization is Δ𝐻vap=29.6 kJ/mol. (b) Calculate the value of Δ𝑆 when 1.00 mol of Br2(𝑙) is vaporized at 58.8  °C.

Verified step by step guidance
1
Identify the formula to calculate the change in entropy (\( \Delta S \)) for a phase change: \( \Delta S = \frac{\Delta H_{\text{vap}}}{T} \).
Convert the temperature from degrees Celsius to Kelvin by adding 273.15 to the given temperature: \( T = 58.8 + 273.15 \).
Substitute the given values into the formula: \( \Delta S = \frac{29.6 \text{ kJ/mol}}{T} \), where \( T \) is the temperature in Kelvin.
Ensure the units are consistent. Since \( \Delta H_{\text{vap}} \) is given in kJ/mol, the result for \( \Delta S \) will be in kJ/(mol·K).
Calculate the value of \( \Delta S \) using the substituted values.

Verified Solution

Video duration:
2m
This video solution was recommended by our tutors as helpful for the problem above.
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enthalpy of Vaporization

The enthalpy of vaporization (ΔH_vap) is the amount of energy required to convert one mole of a liquid into its vapor at constant temperature and pressure. For Br₂, this value is given as 29.6 kJ/mol, indicating the energy needed to vaporize the liquid at its boiling point. Understanding this concept is crucial for calculating changes in entropy during phase transitions.
Recommended video:
Guided course
01:37
Enthalpy of Vaporization Example

Entropy (ΔS)

Entropy (ΔS) is a measure of the disorder or randomness in a system. When a substance transitions from a liquid to a gas, such as Br₂ vaporizing, the entropy increases due to the greater freedom of movement of gas molecules compared to liquid molecules. The change in entropy can be calculated using the formula ΔS = ΔH/T, where ΔH is the enthalpy change and T is the temperature in Kelvin.
Recommended video:
Guided course
02:46
Entropy in Thermodynamics

Temperature Conversion

In thermodynamic calculations, it is essential to convert temperatures from Celsius to Kelvin. The Kelvin scale is used because it is an absolute temperature scale, where 0 K represents absolute zero. To convert Celsius to Kelvin, simply add 273.15 to the Celsius temperature. For the boiling point of Br₂ at 58.8 °C, the corresponding temperature in Kelvin is 331.95 K.
Recommended video:
Guided course
02:10
Temperature Conversion Example
Related Practice
Textbook Question

Indicate whether each statement is true or false. (a) ΔS is a state function. (b) If a system undergoes a reversible change, the entropy of the universe increases. (c) If a system undergoes a reversible process, the change in entropy of the system is exactly matched by an equal and opposite change in the entropy of the surroundings. (d) If a system undergoes a reversible process, the entropy change of the system must be zero.

919
views
Open Question
Indicate whether each statement is true or false. (a) The entropy of the universe increases for any spontaneous process. (b) The entropy change of the system is equal and opposite that of the surroundings for any irreversible process. (c) The entropy of the system must increase in any spontaneous process. (d) The entropy change for an isothermal process depends on both the absolute temperature and the amount of heat reversibly transferred.
Textbook Question

The normal boiling point of Br2(l) is 58.8 °C, and its molar enthalpy of vaporization is ΔHvap = 29.6 kJ/mol. (a) When Br2(l) boils at its normal boiling point, does its entropy increase or decrease?

927
views
Textbook Question

The element gallium (Ga) freezes at 29.8 °C, and its molar enthalpy of fusion is ΔHfus = 5.59 kJ/mol. (a) When molten gallium solidifies to Ga(s) at its normal melting point, is ΔS positive or negative?

1332
views
Textbook Question

The element gallium (Ga) freezes at 29.8 °C, and its molar enthalpy of fusion is ΔHfus = 5.59 kJ/mol. (b) Calculate the value of ΔS when 60.0 g of Ga(l) solidifies at 29.8 °C.

871
views
Textbook Question

Indicate whether each statement is true or false. (c) In a certain spontaneous process the system undergoes an entropy change of 4.2 J/K; therefore, the entropy change of the surroundings must be -4.2 J/K.

265
views