Chemical EquationsChemical Equations

Putting chemical changes Putting chemical changes into wordsinto words

A chemical equation is A chemical equation is a symbolic a symbolic

representation of a representation of a chemical reaction.chemical reaction.

Equation Example:Equation Example:

The burning of methane gas in oxygen is:

CH4 + 2 O2 → CO2 + 2 H2O

Review:Review:Element SymbolsElement Symbols

All elements are represented All elements are represented

by a 1 or 2 letter symbol by a 1 or 2 letter symbol For exampleFor example

• C = CarbonC = Carbon

• Ne = NeonNe = Neon

• O = OxygenO = Oxygen

The symbols are shown on The symbols are shown on

the periodic tablethe periodic table

Chemical FormulasChemical Formulas

Shows the elements & number of Shows the elements & number of atoms of each element in a moleculeatoms of each element in a molecule

HH22SOSO44

ElementsElements

• Hydrogen; 2 atomsHydrogen; 2 atoms

• Sulfur: 1 atomSulfur: 1 atom

• Oxygen: 4 atomsOxygen: 4 atoms

7 atoms total7 atoms total

Subscript

CoefficientsCoefficients

A chemical formula may begin with a A chemical formula may begin with a number.number.

If there is no number, then “1” is If there is no number, then “1” is understood to be in front of the understood to be in front of the formula.formula. This number is called the This number is called the coefficientcoefficient..

CoefficientsCoefficients

The coefficient represents the The coefficient represents the number number of of moleculesmolecules of that of that compound or atom needed in the compound or atom needed in the reaction.reaction.

For example:For example:

• 2H2H22SOSO4 4 – 2 molecules of Sulfuric – 2 molecules of Sulfuric

AcidAcid

CoefficientsCoefficients

2H2H22SOSO4 4 – 2 molecules of Sulfuric Acid– 2 molecules of Sulfuric Acid A coefficient is A coefficient is distributeddistributed to ALL elements in to ALL elements in

a compounda compound• 2 – H2 – H22 (for a total of 4 H atoms) (for a total of 4 H atoms)

• 2 – S (for a total of 2 S atoms)2 – S (for a total of 2 S atoms)

• 2 – O2 – O4 4 (for a total of 8 O atoms)(for a total of 8 O atoms)

Reading Chemical EquationsReading Chemical Equations

Each side of an equation represents a Each side of an equation represents a combinationcombination of chemicals. of chemicals.

The combination is written as a set of The combination is written as a set of chemical formulas, separated by chemical formulas, separated by ++ symbols. symbols.

CHCH44 + 2 O + 2 O22 → CO → CO22 + 2 H + 2 H22OO

Coefficient

Reading Chemical EquationsReading Chemical Equations

The two sides of the equation are The two sides of the equation are separated by an separated by an arrowarrow. . The combination of chemicals The combination of chemicals beforebefore the the

reaction are on the left side of the arrow, reaction are on the left side of the arrow, called the called the reactantsreactants

The right side indicates the combination of The right side indicates the combination of chemicals chemicals afterafter the reaction, called the the reaction, called the productproduct..

For Example:For Example:

In this reaction, sodium (In this reaction, sodium (NaNa) and ) and oxygen (oxygen (OO22) react to make a single ) react to make a single molecule, molecule, NaNa22OO

The The reactantreactant in this equation are in this equation are Na + O2

The The product product in this equation is in this equation is Na2O

Na + O2 → Na2O

Conservation of Mass Conservation of Mass During any chemical reaction, the During any chemical reaction, the

massmass of the of the productsproducts is always equal is always equal to the to the massmass of the of the reactantsreactants..

All the massAll the mass can be accounted for: can be accounted for: Burning of wood results in products that Burning of wood results in products that

appear to have less mass as ashes; appear to have less mass as ashes; where is the rest? where is the rest? Gases and smoke.Gases and smoke.

Law of conservation of massLaw of conservation of mass

Balancing EquationsBalancing EquationsThe Law of Conservation of Mass The Law of Conservation of Mass

states that in a states that in a chemical reactionchemical reaction, , the quantity or the quantity or amountamount of each of each element does not change.element does not change.

This means that each side of the This means that each side of the equation must represent the same equation must represent the same quantity of each element; in other quantity of each element; in other words have the words have the samesame numbernumber of of each kind of each kind of atomatom

Balancing EquationsBalancing EquationsNa + ONa + O22 → Na → Na22O O

ReactantsReactants ProductsProducts Na 1Na 1 Na 2Na 2 O 2O 2 O 1O 1

In order for this equation to be In order for this equation to be balancedbalanced, there must be , there must be equal equal amountamount of of NaNa on the on the leftleft hand hand side and on the side and on the rightright hand side. hand side.

Balancing EquationsBalancing EquationsNa + ONa + O22 → Na → Na22OO

Right now, there is 1 Na atom on Right now, there is 1 Na atom on the left but 2 Na atoms on the the left but 2 Na atoms on the right. We solve this problem by right. We solve this problem by putting a 2 in front of the Na on putting a 2 in front of the Na on the left hand side, Like this:the left hand side, Like this:

2Na + O2Na + O22 → Na → Na22OO

Balancing EquationsBalancing Equations2Na + O2Na + O22 → Na → Na22O O

ReactantsReactants ProductsProductsNa 2Na 2 Na 2Na 2O 2O 2 O 1O 1

Balancing EquationsBalancing Equations2Na + O2Na + O22 → Na → Na22OO

There are 2 Na's on the left and 2 Na's on There are 2 Na's on the left and 2 Na's on the right. But what about the O? the right. But what about the O?

We now must check to see if the O's are We now must check to see if the O's are balancedbalanced on both sides of the equation. on both sides of the equation.

On the left hand side there are 2 O's On the left hand side there are 2 O's and the right hand side only has one. and the right hand side only has one. This is still an This is still an unbalancedunbalanced equation. equation.

Balancing EquationsBalancing Equations2Na + O2Na + O22 → Na → Na22OO

To fix this we must put a To fix this we must put a coefficient of coefficient of 22 in front of the in front of the NaNa22O on the right hand side. O on the right hand side.

Now our equation reads: Now our equation reads:

2Na + O2Na + O22 → 2Na → 2Na22OO

2Na + O2Na + O22 → 2Na → 2Na22O O ReactantsReactants ProductsProducts

Na 2Na 2 Na 4Na 4

O 2O 2 O 2O 2 Notice that the 2 on the right hand side is Notice that the 2 on the right hand side is

"distributed""distributed" to both the Na to both the Na22 and the O. and the O.

Currently the left hand side of the equation Currently the left hand side of the equation has 2 Na's and 2 O's. has 2 Na's and 2 O's.

The right hand side has 4 Na's total and 2 The right hand side has 4 Na's total and 2 O's. O's.

Balancing EquationsBalancing Equations2Na + O2Na + O22 → 2Na → 2Na22OO

Again, this is a problem, there must be Again, this is a problem, there must be an an equalequal amountamount of each chemical on of each chemical on both sides. To fix this let's add 2 more both sides. To fix this let's add 2 more Na's on the left side. The equation will Na's on the left side. The equation will now look like this:now look like this:

4Na + O4Na + O22 → 2Na → 2Na22OO

4Na + O4Na + O22 → 2Na → 2Na22OO Is this balanced?Is this balanced?

ReactantsReactants ProductsProducts

Na 4Na 4 Na 4 Na 4

OO 22 O O 22

Same number of each atom on each side of Same number of each atom on each side of the equation- YES IT IS BALANCEDthe equation- YES IT IS BALANCED

Practice Practice

http://phet.colorado.edu/en/simulation/balahttp://phet.colorado.edu/en/simulation/balancing-chemical-equationsncing-chemical-equations

Khan academy Khan academy http://www.youtube.com/watch?v=RnGu3xhttp://www.youtube.com/watch?v=RnGu3x

O2h74O2h74

Plants make chlorophyll in the plants leaves.

The color changes in autumn leaves are due, in part, to the ending of a chemical reaction. The plants stop making chlorophyll while existing chlorophyll is breaking down. The brilliant colors of fall foliage result when green chlorophyll in leaves breaks down. The colors of other substances in the leaves become visible.

The copper-covered Statue of Liberty has stood in upper New York Bay for more than a 100 years. The green color of the Statue of Liberty comes from a change to the statues copper metal covering. These changes are a result from chemical reactions.

Matter changes whenever energy is added or taken away. In every physical and chemical change, the total amount of energy stays the same. This principle is called the Law of Conservation of Energy.

SourcesSources

http://en.wikipedia.org/wiki/Chemihttp://en.wikipedia.org/wiki/Chemical_equationscal_equations

Chemical Reactions are…Chemical Reactions are…When one or more substances When one or more substances

are changed into new are changed into new substances.substances.

ReactantsReactants- the stuff you start - the stuff you start withwith

ProductsProducts- what you make- what you make

The products will have NEW The products will have NEW PROPERTIES different from the PROPERTIES different from the reactants you started withreactants you started with

Arrow points from the reactants Arrow points from the reactants toto the the new productsnew products