Question

What is the vapor pressure of mercury at its normal boiling point \(\left(357^{\circ} \mathrm{C}\right)\) ?

Short answer

The vapor pressure of mercury at its normal boiling point is 760 mmHg.

Step-by-step solution

Understanding the Concept

The vapor pressure of a substance at its normal boiling point is equal to the atmospheric pressure, which is 1 atmosphere or 760 mmHg for any liquid, as this is the definition of the boiling point.

Applying the Definition

At the boiling point of mercury, the temperature is such that the vapor pressure equals the external pressure, which is 1 atmosphere. This is by definition since boiling occurs when a liquid's vapor pressure matches the external pressure.

Determining the Vapor Pressure

Since the problem asks for the vapor pressure at the normal boiling point, this pressure is the atmospheric pressure at standard conditions, which is 760 mmHg.

Key concepts

Boiling Point

The boiling point of a liquid is a fascinating concept that tells us the temperature at which the liquid turns into vapor. This happens when the vapor pressure of the liquid equals the surrounding atmospheric pressure. When both pressures align, the liquid molecules have enough energy to transition into the gas phase. This process of boiling can be easily observed when water heats to 100°C at sea level.

Boiling is an essential concept in chemistry and physics. Various factors influence it:

• Atmospheric Pressure: Changes in atmospheric pressure alter the boiling point. At higher altitudes, atmospheric pressure is lower, causing liquids to boil at a lower temperature.
• Vapor Pressure: The intrinsic ability of a liquid to evaporate. If a liquid has high vapor pressure, it will boil easier.

Atmospheric Pressure

Atmospheric pressure plays a vital role in determining the boiling point of liquids. It refers to the weight of the atmosphere exerted on a unit area. Generally measured in units such as atmospheres (atm) or millimeters of mercury (mmHg).

At sea level, normal atmospheric pressure is approximately 1 atmosphere (760 mmHg). This standard condition is essential for defining concepts such as the normal boiling point.

• High Atmospheric Pressure: Increases the boiling point, requiring more energy (heat) for the liquid to boil.
• Low Atmospheric Pressure: Decreases the boiling point, making it easier for the liquid to transition into vapor.

Mercury

Mercury is a unique element famous for being a metal that is liquid at room temperature. With a silvery appearance and mirror-like finish, it is often associated with applications such as thermometers and barometers.

When examining mercury's properties concerning vapor pressure, we find that it behaves similarly to other liquids: its vapor pressure increases with temperature. Notably, mercury's normal boiling point is at a high temperature of 357°C. At this point, mercury's vapor pressure matches the standard atmospheric pressure at 1 atmosphere.

• Unique Properties: Like its high density and ability to conduct electricity.
• High Vapor Pressure: Leads to mercury evaporating more readily at higher temperatures.

Normal Boiling Point

The normal boiling point is the temperature at which a liquid boils under normal atmospheric pressure of 1 atmosphere (760 mmHg). It's an essential reference point widely used in scientific research and engineering to characterize substances.

The normal boiling point provides insights into a liquid's characteristics and intermolecular forces. For mercury, its normal boiling point at 357°C gives clues to its strong metallic bonds and high vapor pressure.

• Characterization: Helps classify liquids according to their ease of boiling and molecular interactions.
• Practical Applications: Used in designing equipment like distillation apparatus where precise boiling points are crucial.