Question

Ethanethiol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{SH} ;\right.\) also called ethyl mercaptan) is commonly added to natural gas to provide the "rotten egg" smell of a gas leak. The boiling point of ethanethiol is \(35^{\circ} \mathrm{C}\) and its heat of vaporization is \(27.5 \mathrm{~kJ} / \mathrm{mol}\). What is the entropy of vaporization for this substance?

Short answer

The entropy of vaporization for ethanethiol is approximately 0.0892 kJ/mol·K.

Step-by-step solution

Convert the boiling point to Kelvin

To convert from Celsius to Kelvin, add 273.15 to the given value: Boiling point in Kelvin = 35 + 273.15 = 308.15 K Step 2: Calculate Entropy of vaporization

Use the formula to calculate the entropy of vaporization

Entropy of vaporization = \(\frac{Heat \ of \ vaporization}{Boiling \ point}\) Plug in the given values: Entropy of vaporization = \(\frac{27.5 \ kJ/mol}{308.15 \ K}\) Next, divide 27.5 by 308.15: Entropy of vaporization = 0.0892 kJ/mol·K So, the entropy of vaporization for ethanethiol is approximately 0.0892 kJ/mol·K.

Key concepts

Understanding Ethanethiol

Ethanethiol, known chemically as C\(_2\)H\(_5\)SH, is a volatile sulfur compound. It stands out because it has a strong, pungent smell, often likened to that of rotten eggs. This distinctive odor is not just a random feature; it is deliberately utilized as an additive in natural gas. When natural gas, which is largely odorless, is released into the air during a leak, the scent of ethanethiol acts as an alert to help ensure safety.

Here are some interesting properties of ethanethiol:

• Low boiling point, which facilitates its vaporization at moderate temperatures.
• It is highly reactive, particularly with oxygen, under certain conditions.
• It exhibits both polar and non-polar characteristics due to its structure, affecting its interactions with other compounds.

These properties make ethanethiol not just an interesting compound to study but also a critical safety component in everyday applications.

The Concept of Boiling Point

The boiling point of a substance is the temperature at which it changes from a liquid to a gas. For ethanethiol, this temperature is 35°C, or when converted to Kelvin, 308.15 K. This is particularly interesting because its boiling point is relatively low compared to many other organic compounds.

Some key notes about boiling point:

• It is directly related to atmospheric pressure; lower pressures can result in lower boiling points.
• Intermolecular forces, such as hydrogen bonding or van der Waals forces, significantly affect the boiling point.
• Compounds with similar structures can have significantly different boiling points due to subtle variations in their molecular interactions.

Boiling point is a critical factor in the practical use of ethanethiol, influencing how it can be safely handled and stored.

Exploring Heat of Vaporization

The heat of vaporization is the energy required to convert a mole of liquid into a gas at its boiling point, without changing the temperature. Ethanethiol's heat of vaporization is measured at 27.5 kJ/mol. This value indicates the energy needed to overcome intermolecular interactions and convert ethanethiol into its gaseous form.

Key takeaways about heat of vaporization:

• The stronger the intermolecular forces in a liquid, the higher the heat of vaporization.
• This property is vital for applications involving energy calculations, such as refrigeration and distillation processes.
• Understanding heat of vaporization helps in predicting how a substance will behave under different thermal conditions.

For ethanethiol, this property complements its use in natural gas, as its efficient vaporization contributes to its detection during gas leaks.

Principles of Thermodynamics in Action

Thermodynamics is the study of energy transformations, and it plays a crucial role in understanding physical and chemical changes. In the context of ethanethiol and its vaporization:

• The entropy of vaporization is calculated by dividing the heat of vaporization by the boiling point in Kelvin. For ethanethiol, this calculation gives an entropy change of approximately 0.0892 kJ/mol·K.
• This entropy change reflects the increase in disorder as ethanethiol transitions from a liquid to a gas.
• Thermodynamics also helps explain why certain substances have particular boiling points or vaporization energies, based on the balance of forces and energy exchanges within the system.

Tapping into thermodynamics allows scientists and engineers to predict and optimize the behavior of substances under various conditions, making it essential for many technological applications.