Wednesday January 23, 2013

WednesdayJanuary 23, 2013

(What is Stoichiometry?; Mole

Ratios)

Bell RingerWednesday, 1-23-13

Sodium metal reacts with chlorine gas to produce sodium chloride.

Write the balanced chemical equation.

Na + Cl2 æ NaCl22What do the blue balance numbers really

mean?The blue balance numbers represent either

the number of particles of each substance or the number of moles of each substance.

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Issued Date Due Date Into GradeSpeed Final Day

QUIZ 15 S5 1/11 1/15 1/29

Stoichiometry

What is Stoichiometry?

Stoichiometry involves the quantity relationships between reactants and

products in a chemical reaction.

Stoichiometry is used when you have a problem where you are given the

quantity of one substance and you need to determine the quantity of another

substance.

Stoichiometry can be used to determine how much of a substance to start with as a reactant, or how much of a substance

will be produced in a reaction.

What is Stoichiometry?All reaction stoichiometry calculations start with a

balanced chemical equation.

The coefficients (balance numbers) of the equation

represent the relative numbers of moles of

reactants and of products.

It is extremely important to recognize what the coefficients of a balanced chemical equation represent.

These coefficients can be interpreted to represent two different things:

– the number of particles of each substance in the reaction.

or– the number of moles of each substance in the reaction.

For example, consider the balanced equation below:

H2 + O2 → H2OThis can be interpreted as 2 molecules of hydrogen

gas react with 1 molecule of oxygen gas to produce 2 molecules of water.

or2 moles of hydrogen gas react with 1 mole of oxygen

gas to produce 2 moles of water.

The Dual Meanings of Coefficients

22

A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a

chemical reaction.Mole ratios use the coefficients from a balanced chemical

equation.Example: aluminum oxide decompose to produce aluminum and oxygen gas. Write and balance the

equation.

Al2O3 → Al + O2

This means that 2 moles of aluminum oxide decompose to produce 4 moles of aluminum and 3 moles of oxygen gas.

The mole ratio of Al2O3 to Al is 2:4, or 1:2

The mole ratio of Al2O3 to O2 is 2:3

The mole ratio of Al to O2 is 4:3

Mole Ratios

2 4

3

2

Sample ProblemWhat are the mole ratios when cadmium (II) metal

reacts with hydrobromic acid to produce cadmium (II) bromide and hydrogen gas.

First, Write and balance the equation.

Cd + HBr æ CdBr2 + H2This means that 1 mole of cadmium reacts with 2 moles of hydrobromic acid to produce 1 mole of cadmium (II)

bromide and 1 mole of hydrogen gas.

What is the mole ratio of Cd to H2? 1:1

What is the mole ratio of HBr to CdBr2? 2:1

What is the mole ratio of CdBr2 to H2? 1:1

Mole Ratios

2

WorksheetIntroduction to Stoichiometry

and Mole Ratios