Chemical EquationsChemical Equations

But first some reviewBut first some review

What is a What is a chemical reactionchemical reaction??

►The process by which one or more The process by which one or more substancessubstances change to change to produceproduce one or one or more different more different substancessubstances..

► In a chemical reaction, the original In a chemical reaction, the original substances are called the substances are called the reactantsreactants..

►The substances that are created are The substances that are created are called called productsproducts.. ReactantsReactants ProductsProducts

To be classified as a chemical To be classified as a chemical reaction, a reaction, a chemical changechemical change must must

occur.occur.►What is the evidence of a chemical What is the evidence of a chemical

reaction?reaction? Change in Change in energyenergy►Release of energy as Release of energy as heatheat►Release of energy as Release of energy as lightlight►Production of a Production of a soundsound►Reduction or increase of Reduction or increase of temperaturetemperature►Absorption or release of Absorption or release of electricalelectrical energyenergy

Formation of a Formation of a new substancenew substance►Formation of a Formation of a gasgas►Formation of a Formation of a precipitateprecipitate – – insolubleinsoluble solid solid

►UnexpectedUnexpected change in change in colorcolor►Change in Change in odorodor

►You must always verify to ensure that You must always verify to ensure that a a physicalphysical change didn’t occur change didn’t occur

Helping chemical reactions to Helping chemical reactions to occuroccur

►For a chemical reaction to occur, the For a chemical reaction to occur, the reactants must be reactants must be brought togetherbrought together..

►During chemical reactions, energy is During chemical reactions, energy is either either absorbedabsorbed (endothermic) or (endothermic) or releasedreleased (exothermic). (exothermic).

►As a result, energy can appear as a As a result, energy can appear as a reactantreactant (endothermic) or a (endothermic) or a productproduct (exothermic).(exothermic).

Chemical equations also show Chemical equations also show the physical states and reaction the physical states and reaction

informationinformationSymbolSymbol MeaningMeaning

(s)(s)

(l)(l)

(g)(g)

(aq)(aq)

oror

oror

heat

catalyst

Pd

Substance in the solid stateSubstance in the liquid stateSubstance in the gaseous stateSubstance in aqueous solution“produces” or “yields”Reversible Reaction

Reactants are heatedCatalyst added to speed reaction

With this information, we can With this information, we can now construct chemical now construct chemical

equations.equations.►Chemical equationsChemical equations – a representation – a representation

of a chemical reaction that uses of a chemical reaction that uses symbolssymbols to show the relationship to show the relationship between the between the reactantsreactants and the and the productsproducts..

►Step one – write a Step one – write a word equationword equation Write the names of Write the names of reactantsreactants separated separated

by a plus sign.by a plus sign. Use an Use an arrowarrow to separate the to separate the reactantsreactants

from the from the productsproducts.. Write the names of the Write the names of the productsproducts

separated by a plus signseparated by a plus sign

►Step 2 - Convert the names into Step 2 - Convert the names into formulasformulas. This is known as an . This is known as an unbalancedunbalanced or or skeletonskeleton equation. equation.

►Step 3 - Balance the atoms by Step 3 - Balance the atoms by changing the changing the coefficientscoefficients only only This is how we conserve This is how we conserve massmass and and

obey the law of conservation of obey the law of conservation of massmass

Hints when balancing Hints when balancing equationsequations

1) Use 1) Use coefficientscoefficients to balance atoms to balance atoms involvedinvolved

2) Balanced equations show 2) Balanced equations show mass mass conservationconservation

3) 3) NeverNever change the change the subscriptssubscripts when when balancing an equationbalancing an equation

4) 4) Polyatomic ionsPolyatomic ions can be balanced as a can be balanced as a unitunit

ExampleExample

►When liquid bromine is mixed with When liquid bromine is mixed with aqueous sodium iodide, the result is aqueous sodium iodide, the result is aqueous sodium bromide and solid aqueous sodium bromide and solid iodine.iodine.

Br2 + NaI NaBr

+ I222

Now we have 2 Br on each side, 2 Na on each side and 2 I on each side

What if the formulas are already What if the formulas are already written?written?

Balance the following:Balance the following:

___Na___Na22SiFSiF66 + ___Na + ___Na ___Si + ___NaF ___Si + ___NaF

___NH___NH33 + ___CuO + ___CuO ___N ___N22 + ___Cu + ___H + ___Cu + ___H22OO

641 1

2 33 31

What if the formulas are already What if the formulas are already written?written?

Balance the following:Balance the following:

___(NH___(NH44))22CrCr22OO77 ___Cr ___Cr22OO33 + ___N + ___N22 + ___H + ___H22OO

___AgNO___AgNO33 + ___AlCl + ___AlCl33 ___AgCl + ___AgCl + ___Al(NO___Al(NO33))33

1 1 1 4

3 31 1