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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
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