Diatomic molecules molar mass

NIST also maintains a website called the NIST Chemistry WebBook (http //webbook. nist.gov), which provides access to a broad array of data compiled under the Standard Reference Data Program. This site allows a search for thermochemical data for more than 7000 organic and small inorganic compounds, reaction thermochemistry data for over 8000 reactions, IR spectra for over 16,000 compounds, mass spectra for over 15,000 compounds, UV/VIS spectra for over 1600 compounds, electronic and vibrational spectra for over 5000 compounds, spectroscopic constants of over 600 diatomic molecules, ion energetics data for over 16,000 compounds, and thermophysical properties data for 74 selected fluids. The site allows general searches by formula, name, CAS registry number, author, and stracture and also a few specialized searches by properties like molar mass and vibrational energies. 

A formula tells you what atoms (or ions) are present in an element or compound. So, from a formula you can find the mass of a mole of the substance, or its molar mass. The simplest formula for most elements is simply that element s symbol. For example, the symbol for silver is Ag. The molar mass of elements whose formulas are this simple equals the atomic mass of the element expressed in g/mol. So, the molar mass of silver is 107.87 g/mol. Diatomic elements have twice the number of atoms in each molecule, so their molecules have molar masses that are twice the molar mass of each atom. For example, the molar mass of Br2 molecules is two times the molar mass of Br atoms (2 x 79.90 g/mol = 159.80 g/mol). 

Molecular elements. For elements that occur as molecules, you must know the molecular formula to determine the molar mass. For example, oxygen exists normally in air as diatomic molecules, so the molar mass of O2 molecules is twice that of O atoms ... 

The molar mass M. of nitrogen is 28.02 gmole-i. The rotational characteristic temperature 0, is 2.87 deg and the vibrational characteristic temperature 0 is 3.35 x 10 deg (calculated from data in Herzberg, Molecular spectra of diatomic molecules , Prentice-Hall, 1939). 

Ans. The ideal gas law is not required since the volume occupied by a mole of any gas at STP is 22.4 L. However, the mass of oxygen must be first converted to moles. Oxygen is a diatomic molecule whose molar mass is 32.0 g/mol therefore, 8.00 g represents 0.25 mol. The volume occupied by 8.00 g of oxygen at STP is... 

An unknown gas composed of homonuclear diatomic molecules effuses at a rate that is 0.355 times the rate at which O2 gas effuses at the same temperature. Calculate the molar mass of the unknown and identify it. 

Because we are told that the unknown gas is composed of homonuclear diatomic molecules, it must be an element The molar mass must represent twice the atomic weight of the atoms in the unknown gas. We conclude that the unknown gas is I2. 

The products of the reaction are carbon dioxide (C) and water (D). Compound A has a similar molar mass to carbon dioxide. Compound B is a diatomic molecule. Identify compound B, and support your answer. 

For two substances in the same phase, and with similar molar masses, the substance with the more complex molecular stracture has the greater standard entropy. [Compare the standard entropies of 03(g) and F2(g).] The more complex a molecular stracture, the more different types of motion the molecule can exhibit. A diatomic molecule such as F2, for example, exhibits only one type of vibration, whereas a bent triatomic molecule such as O3 exhibits three different types of vibrations. Each mode of motion contributes to the total number of available energy levels within which a system s energy can be dispersed. Figure 18.3 illustrates the ways in which the F2 and O3 molecnles can rotate and vibrate. 

For example, the molar mass of the diatomic molecule of hydrogen would be... 

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