Boiling Point
CLAIMED FOR EDITING BY 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:
TB = boiling point at the specific temperature
T0 = temperature at which the liquid boils
Boiling Point Elevation Equation
The main mathematical model for this property is the boiling point elevation equation. This equation takes into account the effect that adding a solute to a solvent has on it's boiling point. For example ΔT = i Kbm, where ΔT is the temperature difference that arises from adding the solute, i is the van 't Hoff factor which is equivalent to the number of substances a molecule ionizes into (i.e NaCl is 2, sugar is 1, MgCl2 is 3), Kb is a thermodynamic constant relating to the solvent, and m is the molality.
A Computational Model
Creating a computational model for this equation would be pretty easy, you would first have to initialize the constants, which would be i, Kb, and either m or the information that goes into calculating molality.
K = ???
m = moles of solute/mass of solvent
i = ???
ΔT = i*K*m
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.
Connectedness
Boiling point in itself is very important in many every day processes and especially in my major (chemical engineering). It is a very important property that often helps to solve many problems about a system. 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:
An article out of the Britannica Online Encyclopedia:
External links
See Below
References
[1] Uses of Boiling Point Elevation Boiling Point Elevation Chemistry Basics Melting Point, Freezing Point, Boiling Point Boiling Point of Water