Unit 7 - Chemistry Honors

Mole Ratio

Ratio between the amounts in moles of any two compounds involved in a chemical reaction. Mole ratios are used as conversion factors between products and reactants in many chemistry problems.

Stoichiometry

Stoichiometry is the study of the relationships or ratios between two or more substances undergoing a physical or chemical change (chemical reaction).

Mole Conversions

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Mole

A chemical mass unit, defined to be 6.022 x 1023 molecules, atoms, or some other unit. The mass of a mole is the gram formula mass of a substance.

Empirical Formula

A formula that shows the ratio of elements present in the compound. The ratios are denoted by subscripts next to the element symbols. Glucose has a molecular formula of C6H12O6. It contains 2 moles of hydrogen for every mole of carbon and oxygen. *The empirical formula for glucose is CH2O.

Molecular Mass

A number equal to the sum of the atomic masses of the atoms in a molecule. The molecular mass gives the mass of a molecule relative to that of the 12C atom, which is taken to have a mass of 12. *The molecular mass of C2H6 is approximately 30 or [(2 x 12) + (6 x 1)]. Therefore the molecule is about 2.5 times as heavy as the 12C atom or about the same mass as the NO atom with a molecular mass of 30 or (14+16).

Molecular Formula

An expression which states the number and type of atoms present in a molecule of a substance. There are 6 C atoms and 14 H atoms in a hexane molecule, which has a molecular formula of C6H14

Molar Mass

Number equal to the sum of the atomic masses of the atoms in a molecule. The molecular mass gives the mass of a molecule relative to that of the 12C atom, which is taken to have a mass of 12. The molecular mass of C2H6 is approximately 30 or [(2 x 12) + (6 x 1)]. Therefore the molecule is about 2.5 times as heavy as the 12C atom or about the same mass as the NO atom with a molecular mass of 30 or (14+16).

Percentage Composition

Percent composition is the percentage by mass of each element in a compound. *The percent composition of water is 20% hydrogen and 80% oxygen.

Percent Yield

The amount of product obtained in a chemical reaction. The absolute yield can be given as the weight in grams or in moles (molar yield). The fractional yield, relative yield, or percentage yield are calculated by dividing the amount of the obtained product by the theoretical yield (the unit of measure for both must be the same) *Ex: $C_6H_6 + HNO_3 \rightarrow C_6H_5NO_2 + H_2O$$15.6 g C_6H_6 * \frac{1mol C_6H_6}{78.1 g C_6H_6} * \frac{1mol C_6H_5NO_2}{1mol C_6H_6} *\frac{123.1 g C_6H_5NO_2}{1mol C_6H_5NO_2}=24.6 g C_6H_5NO_2$Therefore, if all C6H6 were converted to product and isolated, we in theory should obtain 24.6 grams of product (100 percent yield) However, 18 grams were isolated, so the percent yield is 73%

Avogadro's Number

The number of particles found in one mole of a substance. It is the number of atoms in exactly 12 grams of carbon-12. This experimentally determined value is approximately 6.022 x 1023 particles per mole.

Formula Mass

The sum of the atomic weights of the atoms in the empirical formula of the compound. The molecular formula for glucose is C6H12O6, so the empirical formula is CH2O. *The formula mass of glucose is (12)+2(1)+16 = 30 amu.