Stoichiometry

The study of chemical changes is at the heart of chemistry. Stoichiometry is the area of study that examines the quantities of substances produced and consumed in chemical reactions.

To understand stoichiometry, you must understand atomic masses, chemical formulas, and the law of conservation of mass.

Balancing equations Balance the following chemical equation: _____C 2 H 4 + _____O 2  _____CO 2 + ____H 2 O

Avogadro’s Number and the Mole A mole of atoms, a mole of molecules, or a mole of anything else all contain Avogadro’s number of objects. Avogadro’s number = 6.02 X 10 23

Converting Moles to Atoms How many oxygen atoms are there in 0.25 moles of Ca(NO 3 ) 2 ?

Molar Mass The molar mass of an element is the mass(in grams) of 1 mole of that element. This is found on the periodic table under the symbol for the element. The molar mass of a compound is the mass of one mole of that compound.

Calculate the molar mass of Ca(NO 3 ) 2.

Calculating the Number of Molecules and Number of Atoms from Mass To convert grams to the number of molecules and atoms, we must use the molar mass and Avogadro’s number as conversion factors.

How many nitric acid molecules are in 4.20 g of HNO 3 ?

Quantitative Information from Balanced Equations The coefficients in a chemical equation represent the relative numbers of molecules in a reaction; these coefficients also represent the number of moles.

In the following reaction, how many moles of CO2 are produced when mol of C 6 H 12 O 6 react? C 6 H 12 O 6 (aq)  2 C 5 H 5 OH 9(aq) + 2CO 2 (g)

There are three steps to calculating quantities of substances produce or consumed in a chemical reaction when given the amount of grams involved instead of moles: 1. Convert grams to moles using the molar mass 2. Determine the number of moles of unknown quantity using the coefficients of the balanced chemical equation. 3. Convert the moles to grams using its molar mass

What mass of O 2 is consumed in the combustion of 1.00 g of propane(C 3 H 8 )?

Limiting reactant The reactant that is completely consumed in a reaction is the limiting reactant. The other reactants are excess reactants. Using our mole to mole ratios, we can determine which reactant is the limiting reactant.

A strip of zinc metal with a mass of 2.00 g is placed in an aqueous solution containing 2.50 g of silver nitrate, causing the following reaction to occur: Zn(s) + 2AgNO 3 (aq)  2Ag(s) + Zn(NO 3 ) 2 Which reactant is limiting? How many grams of Ag will form?