Problem 5 - General Chemistry: Principles and Modern Applications

Question

One of the following substances is a liquid at room temperature and the others are gaseous: \(\mathrm{CH}_{3} \mathrm{OH}\) \(\mathrm{C}_{3} \mathrm{H}_{8} ; \mathrm{N}_{2} ; \mathrm{N}_{2} \mathrm{O} .\) Which do you think is the liquid? Explain.

Step-by-Step Solution

Answer

Methanol (CH3OH) is a liquid at room temperature.

Step 1: Understand the basics

In their natural form, under standard temperature and pressure (STP), i.e. 0°C and 1 atm, propane, nitrogen, and nitrous oxide are all gases. On the other hand, methanol is a liquid under these conditions.

Step 2: Identify the Liquid Substance

So, among the given substances, Methanol, denoted as CH3OH, is the only substance which is a liquid at room temperature.

Key Concepts

Methanol

Methanol, also known as

• methyl alcohol,
• wood alcohol,
• and carbinol,

is a clear, colorless liquid at room temperature. It has the chemical formula \( \mathrm{CH}_3\mathrm{OH} \) and is known for its characteristic alcohol smell. Methanol is widely used in a variety of applications, such as antifreeze, solvent, and fuel.
Its structure includes a hydroxyl group \(-\mathrm{OH}\), which is responsible for its liquid state at room temperature due to hydrogen bonding.
This bonding causes methanol to have significant intermolecular attractions, which in turn affect its state of matter under various conditions. Methanol has a boiling point of about 64.7°C (148.5°F), and a melting point of about -97.6°C (-143.7°F), making it a liquid over a wide range of temperatures compared to many other small molecules.

Room Temperature

Room temperature is a term we often encounter, especially when referring to chemical reactions and physical states of materials. Conventionally, it is considered to be around 20 to 25°C (68 to 77°F).
This range represents the typical indoor temperature in most human environments.
Understanding room temperature is important when predicting the physical state of substances, like methanol, used in everyday applications.
Many liquids and gases behave differently at room temperature compared to when they are at higher or lower temperatures. For instance, at room temperature, water is a liquid because its ambient conditions support the intermolecular forces that maintain its liquid state. Similarly, methanol is also a liquid at room temperature, unlike substances like propane or nitrogen, which are gases.

Standard Temperature and Pressure (STP)

Standard Temperature and Pressure (STP) is a standard set of conditions for measuring the properties of gases, which helps provide consistency across scientific studies. The standard conditions are a temperature of 0°C (273.15K) and pressure of 1 atm (101.3 kPa).
These conditions are useful in chemistry to compare gas behaviors.
Under STP, many gases behave predictably due to the lack of additional energy changes affecting their molecular movement. However, it’s crucial to understand that not all substances respond the same way under STP.

• Methanol, for instance, remains a liquid.
• On the other hand, nitrogen, nitrous oxide, and propane are all gases under these conditions.

This illustrates how different substances can have varied phase states under the same standard conditions. It highlights the unique properties of methanol that allow it to remain liquid under STP, which is primarily due to its hydrogen bonding and molecular structure.