Question

Define the terms boiling point and normal boiling point.

Short answer

The boiling point is the temperature where a liquid's vapor pressure equals its surrounding pressure. The normal boiling point is this temperature at one atmosphere of pressure.

Step-by-step solution

Define Boiling Point

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the external pressure surrounding the liquid. At this temperature, the liquid turns into vapor (or gas).

Define Normal Boiling Point

The normal boiling point is the specific boiling point of a liquid at a pressure of one atmosphere (atm). It is the temperature at which a liquid boils under standard atmospheric conditions.

Key concepts

Normal Boiling Point

The term 'normal boiling point' refers to a very specific circumstance under which a liquid transforms into a gas. It is defined as the temperature at which a liquid's vapor pressure equals the atmospheric pressure when that atmospheric pressure is at exactly one atmosphere (1 atm). This is a standard reference point used in chemistry to compare the boiling temperatures of different substances under standardized conditions.

For instance, the normal boiling point of water is known to be 100 degrees Celsius or 212 degrees Fahrenheit at 1 atm. This standardization allows scientists and engineers to accurately gauge and predict how a substance will act in a 'normal' environment, such as at sea level on Earth. However, if the atmospheric pressure changes, such as at higher altitudes, the boiling point of the liquid will also change.

Vapor Pressure

Vapor pressure is a crucial concept when understanding why liquids boil. It's the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system. In simpler terms, it is the force that molecules of a liquid exert when they escape the liquid to form a gas or vapor.

As the temperature of a liquid rises, the kinetic energy of its molecules increases too. Once enough molecules have sufficient energy to overcome the liquid’s attractive forces, they escape into the air as gas. At the temperature where the vapor pressure equals the external pressure, boiling occurs. Thus, a liquid in an open container boils when its vapor pressure is equal to the atmospheric pressure pushing down on the liquid's surface.

Phase Transition

A phase transition is a process by which a substance changes from one state of matter to another. The boiling point is a prime example of a phase transition, where a liquid turns into a gas. This specific type of phase transition is also known as vaporization. Phase transitions occur because of changes in energy and pressure. For boiling, it is essentially about the transfer of heat energy to the liquid, which causes an increase in molecular motion and consequently increases vapor pressure.

There are other types of phase transitions as well, such as melting (solid to liquid), freezing (liquid to solid), and condensation (gas to liquid). Each has its unique point at which the transition occurs. Understanding these transitions is vital for various applications ranging from meteorology to culinary arts.

Atmospheric Pressure

Atmospheric pressure is the force per unit area exerted against a surface by the weight of air above that surface in the Earth's atmosphere. It is important because it influences the boiling point of liquids. Standard atmospheric pressure is defined as being exactly 1 atm, but it can vary depending on altitude and weather conditions.

At higher altitudes, atmospheric pressure is lower because there is less air above. Consequently, the boiling point of a liquid is also lower at higher elevations. For example, water boils at less than 100 degrees Celsius on a mountain. Understanding this principle is essential for activities like cooking and for industrial processes where precise boiling points are necessary for the desired chemical reactions to occur.