Technical Science Introduction to Chemistry

Technical Science Introduction to Chemistry

Chemical Equations

Chemical Equations

In this tutorial you will…– Analyze a Chemical Equation– Prove a Chemical Equation is Balanced – Explain Reasons for Balancing Equations– Explore Common Chemical Reactions

Analyze a Chemical Equation

A chemical equation is the method used to express what happens during a chemical reaction.

The chemical equation below outlines a familiar chemical reaction. What is this telling you?

One of the main functions of chemistry is to determine what will happen when substances react.

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2Na + Cl2 2NaCl A chemical equation is really just a recipe. It tells you the amounts of specific ingredients that

are required to make a certain amount of a product.


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Let’s take a closer look at that chemical equation.

2Na + Cl2 2NaCl

First, you should notice that the equation is broken into two parts with an arrow.

The arrow represents the chemical reaction.

The “ingredients” on the left side of the equation are called the

Reactants

Reactants

The “results” on the right side of the equation are called the

Products

Products


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Identify the reactants and the products in the following reactions.

N2 + 3H2 2NH3

BaCO3 BaO + CO2

MnO2 + 4HCl MnCl2 + Cl2 + 2H2O

Reactants Products


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Let’s take another look at that chemical equation.

2Na + Cl2 2NaCl

You probably noticed the numbers associated with chemical formulas for the

reactants and the products.

The large numbers in front of the formulas are called Coefficients.

(Coefficients of one are not written out.)

Coefficients

Coefficients tell the number of atoms or molecules that are required for the reaction.

Coefficients are the amounts of the reactants and products.

The coefficients in this equation tell us…Two sodium atoms will react with One chlorine molecule to produce Two molecules of sodium chloride.

The small numbers following the chemical symbols are

called Subscripts.(Subscripts of one are not written out.)

Subscripts

Subscripts tell the number of atoms that are bonded together to makea single molecule of a substance.

They determine the substance itself.

The subscripts in this equation tell us… Na is in elemental form.

2 Cl atoms are bonded to form a molecule of chlorine gas.1 Na is bonded to 1 Cl to make a molecule of sodium chloride.


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What do the chemical equations below tell you?

N2 + 3H2 2NH3 (NH3 is Ammonia)

2MgO + Si 2Mg + SiO2

1 molecule of nitrogen gas reacts with 3 molecules of hydrogen gas to form 2 molecules of ammonia. Nitrogen and hydrogen molecules are each formed from 2 atoms bonded together. Ammonia is formed from 1 N atom bonded to 3 H atoms.

2 molecules of Magnesium Oxide (each with 1Mg bonded to 1 O) react with 1 atom of silicon to form 2 atoms of magnesium and 1 molecule of silicon dioxide (having 1 Si bonded to 2 O)

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Prove a ChemicalEquation is Balanced

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An equation must be balanced to be useful.

Na + Cl2 NaCl

The equation below is not balanced. Can you see what is missing?

There are no coefficients in the equation above. Coefficients determine the amounts of reactant and

product. The amounts of reactant and product are correct

when the coefficients make the equation balance.

22 1

Remember: coefficients of 1 are not written out.

Prove a Chemical Equation is Balanced

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Prove the equation is balanced.

2Na + Cl2 2NaCl

Remember, a balanced chemical equation has the same type and number of atoms on both the

reactant and product sides.

We need to keep track of types and numbers of atoms on each side of the equation. So…

Let’s get organized by creating a table

Atom Reactant Product

First: Identify the all of the different elements that are involved in this reaction.

There are 2 types of atoms: Sodium & Chlorine

NaCl

Second: Count the number of atoms of each type on the reactant side.

You will consider both coefficients & subscripts

The lack of a subscript and the coefficient of 2 on sodium, tells us that there are 2 Na atoms on

the reactant side.

2

The subscript of 2 and the lack of a coefficient on chlorine, tells us that there is one molecule of

chlorine that contains 2 Cl atoms.

2

Third: Count the number of atoms of each type on the product side.


The Coefficient of 2 and the lack of subscripts, tells us there are 2 molecules of sodium chloride.

Each molecule has 1 Na and 1 Cl.

This gives a total of two sodium atoms and two chlorine atoms on the product side.

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This reaction is balanced because there are same number and types of atoms on each side.


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Prove the equation is balanced.

MnO2 + 4HCl MnCl2 + Cl2 + 2H2O

Remember, a balanced chemical equation has the same type and number of atoms on both the

reactant and product sides.

We need to keep track of types and numbers of atoms on each side of the equation. So…

Let’s get organized by creating a table


First: Identify the all of the different elements that are involved in this reaction.

There are 4 types of atoms: Mn, O, H, & Cl

Mn

O

Second: Count the number of atoms of each type on the reactant side.


MnO2 tells us that there is one molecule of this compound and it has

one manganese bonded to two oxygens.

1

4HCl tells us that there are four molecules each having one hydrogen bonded to one chlorine.So there are four hydrogen and four chlorine.

2

Third: Count the number of atoms of each type on the product side.


2H2O tells us that there are two molecules each having one oxygen bonded to two hydrogens.So there are four hydrogen and two Oxygen

MnCl2 tells us there is one molecule that has 1 manganese bonded to 2 chlorines.

So, there is 1Mn atom and 2 Cl atoms.

2

4H

Cl

4

4

1

2

Chlorine shows up in two products MnCl2 & Cl2. Cl2 tells us there is 1 molecule of chlorine gas

with 2 Cl atoms bonded together.

There are a total of 4 chlorine atoms on the product side of the equation;

2 from the MnCl2 and 2 from the Cl2.

4

This reaction is balanced because there are same number and types of atoms on each side.


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Prove the following reaction is balanced.

2NO + 2CO N2 + 2CO2


N

O

C

2

4

2

2

4

2


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P4O10 + 4HNO3 4HPO3 + 2N2O5


P

O

H

4

22

4

4

22

4

N 4 4


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C6H12O6 + 6O2 6CO2 + 6H2O


C

H

O

6

12

18

6

12

18

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Explain Reasons forBalancing Equations

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You know that a reaction is balanced when the coefficients make the number and type of atoms on each side of the equation equal.

You can also prove whether a reaction is balanced. But why is it so important to balance an equation? Why wouldn’t you want to write the equation like

this… Na + Cl2 NaCl There are at least three reasons why it is important

to balance a chemical reaction.

2Na + Cl2 2NaCl

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Look at the unbalanced equation below.

Na + Cl2 NaCl

Notice there are two chlorine atoms on the reactant side but only 1 chlorine

on the product side.

Cl Cl Na Cl

Where did that other chlorine go?It has to go somewhere. It can’t just disappear.

This leads us to a very important law in chemistry.

The Law of Conservation of Matter.This law states that matter can not be

created or destroyed only changed in form.

This means if we start with two atoms of chlorine we must end with two atoms of chlorine.

The unbalanced equation above suggests that an atom of chlorine just disappeared.

This is against the law.

When the proper coefficients are in place and the equation is balanced,

all the atoms can be accounted for.

2

Na Cl

2

Na Na

Now we are following The Law of Conservation of Matter.


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Look at the partially balanced equation below.

2Fe + 3H2O Fe2O3

Notice in this partially balanced equation that the iron and the oxygen are balanced.

Fe Fe O-Fe-O-Fe-OOH H

OH H

OH H

However, the hydrogens from water on the reactant side are not accounted for on the product side.

Where did those hydrogen atoms go?

As it turns out, the hydrogen atoms bonded together to form another product:

Hydrogen Gas (H2)

+ H2

If a chemical equation is not properly balanced, you may miss

a potential product.

Hydrogen gas is odorless and colorless but explosive.

That’s not a product you would want to overlook.

What coefficient in front of the H2 would make this equation balance?

3

H-HH-HH-H


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What does the unbalanced reaction below tell you?

Na + Cl2 NaCl

Remember, chemical equations are recipes. They tell the amounts of the ingredients required

and the amounts of product you can expect.

This reaction, as written, tells you that sodium atoms (Na) react with chlorine gas molecules (Cl2)

to form molecules of sodium chloride (NaCl)

We know the ingredients and products but we don’t know how much of each is needed.The amounts of each substance are determined

by the coefficients that are assigned when the equation is balanced.

2 2

Na Na Cl-Cl Na-Cl Na-Cl

Balancing the equation tell us how much of each reactant is required and how much of each product

will be produced.

An unbalanced equation is like a recipe that tells you all the ingredients but

doesn’t tell you how much of each one to use


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Why is it important to work with a balanced chemical equation?

If an equation isn’t balanced, it implies that atoms suddenly appear or disappear. This goes against the Law of Conservation of Matter

If an equation isn’t balanced, you may miss a product that is not easily observed.

An equation is a chemical recipe. If it isn’t balanced, it is like a recipe that doesn’t include any amounts. It would be useless to try to make something from such a recipe.

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A chemical reaction is a recipe that lists amounts and type of both reactants and products.

In this section you will analyze common chemical reactions.

The goal is to give you the background information necessary to determine the type of product when given the reactants.

There are seven of these reactions. You have already had experience with some of them.

The following slides will present each of these common chemical reactions.

Explore Common Chemical Reactions Home

2 of 16Explore Common Chemical Reactions

Metal + Nonmetal Salt

Salt Formation

Metals combine with nonmetals to form salts. A specific example is shown above with

sodium metal reacting with chlorine gas.

Na + Cl2 NaCl22

There is a special case of this type of reaction.Metals react with Oxygen (a nonmetal)

to form a Metal Oxide (a salt)

Fe + O2 Fe2O32 34

Metals combining with oxygen is also called corrosion or oxidation. This reaction can be a

costly one because degrades metal objects.

In the specific example above, Iron reacts with Oxygen to form Iron III Oxide.

Which is commonly known as rust.

Most metal objects must be protected from oxygen so this reaction doesn’t occur.

This is one reason for painting metal objects.

3 of 16Explore Common Chemical Reactions What product would be formed from the reactants

listed below.

Mg + O2

Mg (magnesium) is a metal. O2 (oxygen) is a nonmetal.

Metals combine with nonmetals to form salts.


In this case, the salt that forms will be a metal oxide

because the nonmetal is oxygen.

MgO

The product is Magnesium Oxide (MgO)Mg takes on a +2 charge & O is –2.

So one Magnesium balances one Oxygen.

The chemical equation is balancedwith the coefficients shown above.

22

(Metal Oxide)(Oxygen)

Explore Common Chemical Reactions

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Base Formation

Metal Oxide + Water Base

You now know that a metal oxide is a salt.It is composed of a metal bonded to oxygen.

You also know water is H2O.

Na2O + H2O

Remember a base is type of compound that has a metal bonded to the Hydroxide Ion (OH –1).

Here, the metal is sodium (Na+1)

The base that is formed is Sodium Hydroxide.Na has a +1 charge & OH has a –1 charge

so the formula is NaOH. (one Na with one OH)

NaOH

Bases represent an important class of compounds. When you hear the term caustic or alkaline, it is probably in reference to a base.


listed below.

CaO + H2O

CaO (calcium oxide) is a Metal Oxide. H2O is Water.

Metal Oxides combine with water to form bases.


Ca(OH)2

The product is Calcium Hydroxide (Ca(OH)2)Ca takes on a +2 charge & OH is –1.

So one Calcium balances two Hydroxide ions.

The chemical equation is balancedas it is shown above.


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Acid Formation

NonmetalCompound

Nonmetal compounds are two or more nonmetals covalently bonded.You also know water is H2O.

SO3 + H2O

Remember an acid is type of compound that has a Hydrogen ion(s) bonded to a nonmetal.

Here, the nonmetal is the sulfur trioxide (SO3)

The acid that is formed is Sulfuric Acid.H has a +1 charge & SO4 has a –2 charge.

The formula is H2SO4. (two H+ with one SO4-2)

H2SO4

Acids are another important class of compounds. You have heard of various acids;

stomach acid, acid rain, battery acid, acetic acid (vinegar), citric acid (in fruits),

ascorbic acid (vitamin C), etc

+ Water Acid


listed below.

CO2 + H2O

CO2 (carbon dioxide) is a nonmetal compound. H2O is Water.

Nonmetal compounds combine with water to form acids.

NonmetalCompound

+ Water Acid

H2CO3

The product is Carbonic Acid (H2CO3)H takes on a +1 charge & CO3 is –2.

So two Hydrogens balance one Carbonate ion.

The chemical equation is balancedas it is shown above.


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Neutralization

Acid + Base Salt + Water

An acid releases hydrogen H+1 ions.A base releases hydroxide OH-1 ions.

The acid in this case is HCl. The base is NaOH.

HCl + NaOH

A salt is a metal bonded to a nonmetal. The metal is the Na+1 from the base.

The nonmetal is the Cl-1 from the acid. These ions form the salt NaCl

The water forms from the remaining ions. The H+1 (from the acid) bonds to

the OH-1 (from the base). This makes H-OH or H2O (water).

NaCl

The H+ ions of acids and the OH- ions of bases make them very reactive compounds.

But when they react together, the H+ ions and the OH- ions bond tightly to each other.

+ HOH

This forms water which is very stable.The acid and the base “neutralize” each other.

This reaction is often called neutralization.

When you take an antacid for an upset stomach, what you are really doing is

neutralizing your stomach acid with a base (the antacid).

You probably also noticed that in this reaction the pairs atoms traded partners.

The H from the acid bonded to the OH from the base.The Na from the base bonded to the Cl from the acid.

The pairs of atom replaced each other to form two new substances.

This type of reaction is sometimes called a double replacement reaction.


listed below.

HCl + Mg(OH)2

HCl is an acid. Mg(OH)2 is a base. Acids react with bases to form

a Salt and Water.


MgCl2

One product, the salt, is Magnesium Chloride (MgCl2)

Mg takes on a +2 charge & Cl is –1.So, one Magnesium balances two Chlorines

The other product, the water, is H-OHThe H (from the acid) takes on a +1 charge.The OH (from the base ) has a –1 charge.

So, water is HOH or H2O.

+ HOH


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Metal Plating

1st Metal + Salt 2nd Metal + Salt

The metal is in solid elemental form.The salt is dissolved water as ions

The metal here is Zn. The salt is CuSO4.

Zn + CuSO4

The second metal (product) comes from the metal portion of the original salt.

The salt that is produced is formed from the original metal and the nonmetal portion of the

original salt.

Cu

You can see the original metal (the zinc), took the place of the copper in the salt.

We started with Copper II Sulfate & ended with Zinc Sulfate.

+ ZnSO4

The zinc replaced the copper. This type of reaction is often called a single

replacement reaction.

This type of reaction is very common.It is found in batteries and metal plating.

However, it will only occur if the original metal is more reactive than the metal in the salt.

Zinc is more reactive than copper so this reaction will take place.

If copper metal was placed in a solution of zinc sulfate, nothing would happen.


listed below. (Magnesium is more reactive than Silver)

Mg + AgNO3

Mg is a metal. Ag(NO3)2 is a salt. Metals can react with salts producing

a new salt by replacing the metal.

Metal 1 + Salt Metal 2 + Salt

Ag

One product, the metal, is Silver (Ag)The silver was replaced by the magnesium.

Mg donated its e- becoming a Mg+2 ion.The Ag+1 ions accepted the e- and

went back to elemental form.

The other product, the salt, is Mg(NO3)2

The magnesium is now an ion Mg+2 and with two nitrate ions NO3

-1 forms a new salt. (Magnesium Nitrate)

+ Mg(NO3)2


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Combustion

Organic compounds contain carbon.In this case, it is methane gas (CH4) Oxygen is simply Oxygen Gas (O2)

CH4 + O2

One product is Carbon Dioxide (CO2)The other product is Water (H2O)

CO2

This is a reaction that you encounter daily. The reaction of organic compounds with oxygen

to produce carbon dioxide and water is called combustion.

+ H2O

Another word for combustion is burning.This reaction allows us to release energy from

organic fuel sources.

These fuels may be the gasoline in your car, the natural gas that heats your home, coal, oil or

the food you eat to power your body.The basic reaction is the same for each.


Organic Compound

+ Oxygen Carbon Dioxide

+ Water

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listed below.

C3H8 + O2

C3H8 (propane) is an organic compound.It reacts with oxygen in a combustion reaction

to form carbon dioxide and water.

OrganicCompound

+ Oxygen Carbon Dioxide

CO2

The two products in any combustion reaction are always Carbon Dioxide and Water.

There is an additional product in combustion reactions and that is energy.

The production of energy is the reason we burn these fuels.

+ H2O


35

+ Water

4


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Polymerization

Monomer + Monomer Polymer

A monomer is a relatively small molecule.The monomers in this example are

vinyl chloride molecules C2H3Cl

C2H3Cl + C2H3Cl

Small molecules are bonded together to form larger molecules. The groups of monomers are

called polymers.

The polymer that is formed in this case is a chain of vinyl chloride molecules.

It is called Polyvinyl Chloride (PVC).

-[C2H3Cl]-[C2H3Cl]-

The process of putting small molecules (monomers) together to form larger molecules

(polymers) is called polymerization.

The process of polymerization is used to make create synthetic substances like plastics, nylon,

styrofoam, etc.

Polymerization is also used by living things.Proteins are polymers of amino acids. Starch and cellulose are polymers of simple sugars.


listed below.

C2F4 + C2F4

C2F4 are monomers. Monomers combine to form Polymers.

Monomer(Tetrafluoroethylene)

+ Monomer Polymer(Teflon)

-[C2F4]-[C2F4]-

The product is Teflon.It is a polymer of the small C2F4 monomers.

Name Salts with Multivalent Metals

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Write the general reactants and products Formation of a Salt

Formationof a Base

Formationof an Acid

Neutralization

MetalPlating

Combustion

Polymerization



Nonmetal Compound + Water Acid


Metal 1 + Salt Metal 2 + Salt

Organic + Oxygen Carbon + WaterCompound Dioxide

Monomer + Monomer Polymer

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Technical Science Introduction to Chemistry

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Chemical Equations

Created by John W. Pluemer

Technical Science Introduction to Chemistry

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