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From Wikipedia

Mole fraction

In chemistry, mole fractionx is a way of expressing the composition of a mixture. The mole fraction of each component i is defined as its amount of substancenidivided by the total amount of substance in thesystem, n

x_i \ \stackrel{\mathrm{def}}{=}\ \frac{n_i}{n}

where

n = \sum_i n_i \,

The sum is over all components, including the solvent in the case of a chemical solution. As an example, if a mixture is obtained by dissolving 10 moles of sucrose in 90 moles of water, the mole fraction of sucrose in that mixture is 0.1.

The same value for the mole fraction ratio is obtained using the number of molecules of i, Ni, and the total number of molecules of all kinds, N, since

N_i = n_i\, N_{\rm A}\,

where NA is the Avogadro constant≈ 6.022 mol. By definition, the sum of the mole fractions equals one, a normalization property.

\sum_i x_i \ \stackrel{\mathrm{def}}{=}\ 1 \,

Simple representation

The simple representation of examining the mole fraction is thinking in terms of A and B. The mole fraction of A would be moles of A divided by the moles of A and moles of B. This way, adding the two mole fractions together would equal one.

\mathrm{Mole\ fraction\ of\ A} =\frac{\mathrm{Moles\ of\ A}}{\mathrm{Moles\ of\ A\ +\ Moles\ of\ B}}

Another representation would be:

\mathrm{Mole\ fraction\ of\ A}=\frac{nA}{nA + nB}

Where nA is the number of moles of substance A and nB is the number of moles of substance B

Notes and qualifications

Mole fractions are dimensionless numbers. Other ways of representing concentrations, e.g., molarity and molality, yield dimensional quantities (per litre, per kilogram, etc.). When chemical formulas seem to be taking the logarithms of dimensional quantities, there is an implied ratio, and such expressions can always be rearranged so that the arguments of the logarithms are dimensionless numbers, as they must be.

Mole fractions are one way of representing the concentrations of the various chemical species. They are an ideal-mixture approximation to the effect of concentration on the equilibrium or rate of a reaction. In practice (except for very dilute solutions or for gases at atmospheric pressure), all measures of concentration must be multiplied by correction factors called activity coefficients in order to yield accurate results.

The mole fraction is sometimes denoted by the lower case Greek letter χ (chi) instead of aRomanx. For mixtures of gases, it is more usual to use the letter y. The mole fraction of a substance in a reaction is also equal to the partial pressure of that substance.

Mole fraction is based upon moles of substances, not moles of ions. For example, 4 moles of NaCl would not be dissociated into 4 moles of sodium ions and 4 moles of chloride ions.



From Yahoo Answers

Question:Across 1 Number of moles of ammonia produced by the reaction of three moles of nitrogen with excess hydrogen gas. Hint: Balance the equation! 4 Number of moles of hydrogen atoms in two moles of water. 5 Number preceding the molecular formuIa of a reactant or product in a balanced chemical equation, it is usually interpreted as the number of moles of the substance involved in the reaction. 7 Example: For water, this is 11.1% hydrogen and 88.9% oxygen; also known as mass percent (2 words). 9 The number of moles of a compound is calculated by dividing the mass of the pure substance in grams by this term (2 words). 10 Mass in grams, rounded to the nearest whole number, of two moles of helium. 11 Chemical symbols groups in a way that give the exact number of different atoms of an element in a molecule; example is H,SO, (2 words). 12 Simplest whole number ratio of atoms in a compound (2 words). 15 Used with yield, this adjective describes the maximum amount of product that can be formed in a chemical reaction, assuming the mole ratios from the balanced chemical equation. 16 The value of this term for an ideal gas at standard temperature and pressure is 22.4 liters per mole (2 words). 17 Instrument used to determine the relative masses of atoms based on the deflection of ions in a magnetic field (2 words). 18 Adjective used to describe reactant that is "leftover" after a chemical reaction has proceeded to completion because there are a greater number of moles of this reactant than are required by the mole ratio. Down 1 Derived from two Greek words, this term may be translated as "measuring elementsu-it describes the mathematical proportions of reactants and products in a chemical reaction. 2 "Matter cannot be created or destroyed" is a common paraphrase for this Iaw (3 words). 3 Relative number of moles of any two substances in a balanced chemical equation (2 words). 6 Weighted average of the masses of the naturally occurring isotopes of an element (2 words). 7 Calculated by dividing the mass of product obtained in a chemical reaction by the maximum amount predicted based on stoichiometry, and multiplying by 100 (2 words). 8 Adjective used to describe a reactant that is completely used up in a chemical reaction; multiplying the number of moles of this reactant by the mole ratio defines the maximum amount of product that can be obtained. 13 Although his "number" is widely celebrated in chemistry today, the 1811 hypothesis of this obscure Italian chemist was ignored for more than 50 years. 14 The most common isotope of this element is assigned a mass of exactly 12 amu and is used as the standard to calculate the masses of all other atoms. 15 Number of moles of atoms in 48.6 g of magnesium metal. 16 The definition of this fundamental concept in chemistry makes it possible to "count" atoms or molecules by weighing elements and compounds, respectively. If you could help me with any of these I would really appreciate it!!! Thanks again<3333

Answers:wow someone doesn't want to do their homework. If you can't do these you are going to fail miserably. Here are my mole links, teach yourself. http://www.kentchemistry.com/links/MathofChemistryLinks.htm

Question:The mole concept is important in chemistry because 1. atoms and molecules are very small and themole concept allows us to count atoms and molecules by weighing macroscopic amounts of material. 2. it establishes a standard for reaction stoi- chiometry. 3. it explains the properties of gases. 4. it provides a universally accepted stan- dard for mass. 5. it allows us to distinguish between ele- ments and compounds.

Answers:number 1.

Question:Lets say that I have no idea what Avogadro's number, equivalent weight, or any other basic chemistry concept is... how would you explain the concept of a Mole to me then? So, what is a Mole (in layman's terms)?

Answers:One mole of any substance is hte total number of atoms of any given substance as given by the avogadro number which is 6.0221415 10^23 6.0221415 10^23 atoms of hydrogen is one mole of HYDROGEN 6.0221415 10^23 atoms of plutonium is one mole of PLUTONIUM 6.0221415 10^23 grains of sand is one mole of SAND GRAINS 6.0221415 10^23 hairbrushes is one mole of HAIRBRUSHES. 6.0221415 10^23 moles that live in the ground is one mole of MOLES 6.0221415 10^23 stars are one mole of STARS See where this is going? Now the mass of hydrogen and plutonium will be different so you will get different results in equations if and when it comes to doing them. 6.0221415 10^23 elven angels is one mole of Elven angel which would give us at yahoo answers 6.0221415 10^23 questions on moles.... which would be one mole of questions on moles... Lol I got carried away as usual :D

Question:A solution of phenol (C6H5OH) in ethyl alcohol (C2H5OH) is 21.5% phenol by mass. What is the mole fraction of Phenol in the solution.Please give me the formula with its answer of this question for that I can answer the question from another problem please.

Answers:molecular wt of phenol=94 wt of phenol in soln=21.5(percentage by wt.) mole fraction=wt of subst/mol wt of subst =21.5/94 =0.22872

From Youtube

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