Problem 47 - Introductory Chemistry Atoms First

Question

Propane has a boiling point below room temperature, and hexane has a boiling point above room temperature. In what physical state would you expect to find each substance at room temperature (which is usually about \(\left.20{ }^{\circ} \mathrm{C}\right) ?\)

Step-by-Step Solution

Answer

At room temperature (20°C), propane's boiling point is below 20°C, making it a gas, while hexane's boiling point is above 20°C, making it a liquid.

Step 1: Understanding the boiling points of Propane and Hexane

Given that propane has a boiling point below room temperature (20°C) and hexane has a boiling point above room temperature, we can conclude that at room temperature, propane has already reached and surpassed its boiling point and hexane has not.

Step 2: Determine the physical state for Propane

Propane's boiling point is below 20°C, which means that propane has already reached its boiling point before the room temperature. Therefore, propane would have turned into a gaseous state at room temperature (20°C).

Step 3: Determine the physical state for Hexane

Hexane's boiling point is above 20°C, which means that hexane has not reached its boiling point at room temperature. Thus, it remains in a liquid state at room temperature (20°C).

Step 4: State the conclusion

In conclusion, propane would be in the gaseous state, and hexane would be in the liquid state at room temperature (20°C).

Key Concepts

Boiling Point

The boiling point of a substance is the temperature at which it transitions from a liquid to a gas. This is a key property of matter and is crucial for identifying its state under various conditions. Each substance has its unique boiling point. For instance, water boils at 100°C, under standard atmospheric pressure.
Understanding boiling points is crucial when considering the physical state of a substance at a given temperature. If the surrounding temperature is higher than the boiling point of that substance, it will exist as a gas; if it's lower, the substance will remain liquid or solid based on additional factors like the freezing point.

• Boiling points are pressure-dependent: The boiling point can change with varying atmospheric pressures.
• Pure vs. mixture: The presence of impurities or the substance being part of a mixture can elevate or depress the boiling point.
• Identifying state of matter: Knowing the boiling point helps to predict the state of matter, just like with propane and hexane in our example.

Room Temperature

In scientific terms, room temperature is generally considered to be about 20°C to 25°C (68°F to 77°F). This is the standard temperature often assumed when discussing the physical properties of substances under 'normal' conditions.
It's important because it represents the average condition in which most indoor activities occur, and it's the baseline temperature used to predict the behavior of substances. For example, when scientists or chemists speak of a reaction occurring at room temperature, they're referring to this range.
When considering the state of matter of compounds like propane and hexane at room temperature, we make predictions based on how their boiling points compare to this standard temperature range.

State of Matter

The state of matter refers to the distinct forms that different phases of matter take on. The most familiar states are solid, liquid, and gas. Propane and hexane, being different substances, each have their respective states of matter at room temperature.

• Solid: Retains a fixed shape and volume, with particles that are closely packed together.
• Liquid: Has a definite volume but takes the shape of its container, with particles that are close but can move past each other.
• Gas: Doesn't have a fixed shape or volume, with particles that move freely and spread out evenly in a container.

The state of matter of a substance at room temperature can thus be understood by its boiling point in relation to room temperature. Since propane boils below room temperature, it will be a gas, while hexane, boiling above room temperature, stays in a liquid state.
This understanding aides in many practical situations, such as storage and transportation of substances, where their physical state at room temperature determines the necessary conditions and equipment.