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Boiling And Melting Points Essay

3963 words - 16 pages

2nd Quarter / SY 2012-2013

Engr. Josephine A. Ng

CHM142L / B21
Novhanda, Michelle
Group No. 6

Experiment No. 1

One of the methods to identify an organic compound is by determining its physical properties. In this experiment, we will only looking for their melting point and boiling point on the effects of the chemical structures. Melting point is defined as the temperature at a specific pressure which the solid and liquid phases are in equilibrium with each other. The boiling point is used to characterize a new organic liquid and knowledge of the boiling point helps to compare one organic ...view middle of the document...

In other words, pure substance has higher melting point than the impure. The trans-isomers (fumaric acid) is also have higher melting point due to its greater stability compared to cis-isomers (maleic acid). Branching of organic compound will decrease boiling point as branched molecules have weaker dispersion forces, unlike the straight chains. Therefore, straight chains have higher boiling point since more energy is needed to break the intermolecular attraction.

Physical properties can be observed or measured without changing the composition of matter. Physical properties are used to observe and describe matter. Often, a compound may be identified simply by determining a number of its physical properties.
Physical properties include appearance, texture, color, odor, melting point, boiling point, density, solubility, polarity, and many others. Two of the most commonly recognize physical properties of a compound are boiling point and melting point.
The three states of matter are solid, liquid, and gas. The melting point and boiling point are related to changes of the state of matter. All matter may exist in any of three physical states of matter.
The Melting point is the temperature at which the solid phase changes over to the liquid phase. Melting point, unlike boiling point, is a solid state property and hence is influenced by properties of solids such as amorphous or crystalline nature, allotropy, polymorphism, molecular symmetry, as additional and more important factors than intermolecular forces.
The boiling points of organic compounds can give important clues to other physical properties and structural characteristics. A liquid boils when its vapor pressure is equal to the atmospheric pressure. Vapor pressure is determined by the kinetic energy of molecules. When the temperature reaches the boiling point, the average kinetic energy of the liquid particles is sufficient to overcome the forces of attraction that hold molecules in the liquid state.
The physical properties of a compound are determined by the attractive forces between the individual molecules, called Intermolecular Forces. It is often difficult to predict a precise melting pint or boiling pint or biling pint for a compound. All intermolecular forces are electrostatic, that is, these forces occur as a result of the attraction between opposite charges. There are the four types of intermolecular forces: ion-ion, ion-dipole, dipole-dipole, and London dispersion forces or van der Waals forces. Hydrogen bonding is under dipole-dipole branch.
Ion-ion interactions are the strongest. Since a large amount of heat energy must be provided to disrupt these forces, ionic compounds typically have high melting and boiling points. Ion-dipole interaction is the force of attraction between an ion and a polar molecule. Dipole-dipole interactions are the electrostatic attractions between polar molecules, which align in such a way that the opposite poles are in proximity....

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