stoichiometry_1

7/27/2019 STOICHIOMETRY_1

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Stoichiometry


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Just what is stoichiometry?

The word stoichiometry is derived

from two Greek words: stoicheion(meaning element) and metron

(meaning measure).


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How does it work?

Then the chemist uses the equation to

guide them in calculating theproducts. Since stoichiometry is used

to predict things in the perfect

world, we can expect that thereaction in real life wont create the

maximum amount of product.


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The chemical equation is the

chemists recipe!

By using the chemical equation, chemists can

calculate the amount of materials needed orthe approximate amount of materials produced

(the amount of materials actually produced in

the lab is approximate since we do not live in a

perfect world).


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How do I use the chemical

equation?

The chemical equation is written like a

mathematical expression. When balanced, thecoefficients tell how many moles of each

reactant or product is needed or expected.


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Example:

2H2 + O2 2H2O

One way to understand the information conveyed by

a chemical equation is to convert the equation into

an English sentence.


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So: 2H2 + O2 2H2O

This equation really says: two moles of H2

added to one mole O2 yields two moles ofwater.

(the coefficients tell how many moles, atoms or

molecules of each chemical are needed in therecipe)


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Quantitative Information from

Balanced Equations

In addition to being both a qualitative and

quantitative statement of fact, a balancedchemical equation is an algebraic equality in

which the arrow is the equal sign. This means

that we can manipulate a balanced chemicalequation in much the same way as we can

manipulate any other algebraic equality.


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Consider the combustion of propane.

C3H8 + 5 O2 3CO2 + 4H2O


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Stoichiometry has 5 basic steps:

Step 1: Write and balance the equation


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Step 2: Write in all information given

(make sure to identify what you aretrying to find!)


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Step 3: Convert everything to moles


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Step 4: Use mole ratio to solve for what

you are trying to find (you may alsouse a proportion to solve the

problem.)


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Step 5: Convert everything into the

required unit if needed.


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What is a mole ratio?

Mole Ratios: The mole ratio is based on

the balanced chemical equation.


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Example of a mole ratio:

CH4 + 2O2 CO2 + 2H2O

The mole ratio of CH4:O2 is 1:2. Another

way to write this is CH4.2O2


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How do you use a mole ratio?

The mole ratio is an equivalent which

means that you can arrange the ratioin any way needed.


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Example of a mole ratio problem:

N2 + 3H2

2NH3

Write the molar ratios for N2 and H2.Write the molar ratios for NH

3and H

2.

Convert the ratios above into afraction.


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Examples of a mole-mole

stoichiometric problem:

2H2 + O2 2H2O

1. How many moles of H2O are

produced when 5 moles of oxygen are

used?


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Examples of a mole-mole

stoichiometric problem continued:

2H2 + O2 2H2O

2. If 3.00 moles of H2O are produced,

how many moles of oxygen must beconsumed?


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Example of a mole-mass

stoichiometric problem:

2H2 + O2 2H2O

If 3.00 moles of oxygen are completely

converted to water, what is the mass of

the water produced?

stoichiometry_1

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