Boiling Point

Claimed for editing: Shreenu Sivakumar

The Main Idea

Boiling point is a key property of matter in which the vapor pressure of a liquid equals the pressure around the liquid and the liquid turns into a vapor. The boiling point of a substance is highly dependent on the environment around the substance. For example, at a high pressure a liquid has a higher boiling point than it would have at atmospheric pressure. Similarly, at low pressure a liquid has a lower boiling point. Another environmental factor that affects the boiling point of a liquid is whether the liquid is in a partial vacuum. In this state, the boiling point of a liquid will be lower than the boiling point of the same liquid at atmospheric pressure. In addition, different liquids boil at different temperatures for a set pressure.

A Mathematical Model

There are several equations that relate to boiling point, including the Clausius–Clapeyron equation and the boiling point elevation equation.

Clausius-Clapeyron Equation

This equation should be used when the vapor pressure and heat of vaporization for the liquid are known for a specific temperature and you are trying to calculate the boiling point.

The constants in the equation can be defined as:

T_B = boiling point at the specific temperature

T₀ = temperature at which the liquid boils

R = ideal gas constant, 8.3144598 J * [math]\displaystyle{ mol^{-1} }[/math] * [math]\displaystyle{ K^{-1} }[/math]

P = vapor pressure at the specific pressure given

P₀ = pressure that corresponds to the T₀ used

ΔH_vap = heat of vaporization of the liquid

Boiling Point Elevation Equation

This equation accounts for a solution's boiling point being higher than just the solvent's boiling point. This equation should be used when The equation is:

ΔT_b = K_b· b_B

The constants in the equation can be defined as:

ΔT_b = boiling point elevation, which is equal to T_{b, solution} - T_{b, solvent}

K_b = Ebullioscopic constant

b_B = Molality of the solution, b_B = b_solute · i

A Computational Model

Creating a computational model for this equation would first include initializing the constants below:

K_b =

b_B = b_solute · i

i =

b_solute =

From here the equation can be used:

ΔT_b = K_b· b_B

Examples

An example of an easy, middling and difficult problem are included in the link below. An easy example would be problems 3-5, a middling example would be problems 6, 8, 9, and 10. A difficult example would be the bonus problems.

Boiling Point Elevation

Connectedness

Boiling point in itself is very important in many every day processes. It is a very important property that often helps to solve many problems about a system, especially in chemical engineering. One universal use for boiling point elevation is in cooking. Adding a solute such as salt to water that you are trying to boil will cause it to be hotter than it would be otherwise when the boiling point has not been elevated. A large amount of solute would be necessary to acquire an appreciable increase, however there is a very small increase no matter how much you use. Boiling point elevation is also used in sugar refining; at some points during the process the syrup is boiled and the temperature at which it boils depends on the concentration of sugar at that time.

History

In 1741, Anders Celsius defined his temperature scale on the melting and boiling temperature of water. Although Celsius did not discover the thermometer – both Philo and Hero of Alexandria (who also mentioned steam power in 50 BC) described such a principle – his design was much more precise than any previous such invention. Celsius scaled his measurements as 0 for boiling point and 100 for freezing point but the order was later reversed.

See also

For information on melting point, a very similar property, see Melting Point

Further reading

An article from Purdue:

Boiling

An article out of the Britannica Online Encyclopedia:

Boiling Point

External links

[1]

References

Uses of Boiling Point Elevation [2] Boiling Point Elevation Chemistry Basics Melting Point, Freezing Point, Boiling Point Boiling Point of Water