Chemical Formulas & Equations Ch 14.2 8th

8/8/2019 Chemical Formulas & Equations Ch 14.2 8th

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Ch 14 Section 2


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Objectives:y Interpret and write simple chemical formulas

yWrite and balance simple chemical equations

y Explain how a balanced equation shows the law ofconservation of mass


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Chemical Formulas:y Ashorthand way to use chemical symbols & numbers

to represent a substance

y It shows how many atoms of each kind are present in amolecule

y Formula for water: H2O one water molecule is madeup of 2 hydrogen atoms and one oxygen atom

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Chemical Formulas:y Subscripts: a # written below and to the right of a

chemical symbol in a formula

y

Example: H2O the 2 is the subscript; only 1 atom ofoxygen is present

y Example: Glucose C6H12O6 - 6 atoms of carbon, 12atoms of hydrogen, 6 atoms of oxygen

http://fitnesslifestylehealthclub.com/wp-content/uploads/2009/08/glucose-molecule.gif


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Chemical Formulas:yWriting formulas for Covalent Compounds:

y Composed of 2 nonmetals

y Names use prefixes, representing a #y Tells how many atoms of each element are in a formula

y Examples: CO2 carbon dioxide one carbon atom, 2

oxygen atomsy Example: N2O dinitrogen monoxide 2 nitrogen

atoms, 1 oxygen atom

http://www.windows2universe.org/physical_science/chemistry/co2_molecule_big.gif


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Chemical Formulas:yWriting formulas for Ionic Compounds:

y Composed of one nonmetal & one metal

y Charge is zeroy The formula has subscripts that cause the charges of the

ions to cancel out

y Example: NaCl sodium chloride 1 sodium atom, 1chlorine atom

y Example: MgCl magnesium chloride 1 magnesiumatom, 2 chlorine atoms

http://www.teachers.ash.org.au/jfuller/chemistry/magnesiumchloride.gif


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Chemical Equations:y Away to describe reactions

y Chemical symbols and formulas are used

y Starting material: reactants

y Substances formed from a reaction: products

y Example: C + O2 CO2


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Chemical Equations:y The importance of accuracy

y Formulas and symbols can be mistaken

y Similar symbols & formulas

y CO2 carbon dioxide

y CO carbon monoxide

y Co the element cobalt

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http://www.buzzle.com/img/articleImages/276131-8511-16.jpg


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Chemical Equations:y Must be balanced

y Atoms cannot be lost or gained in a chemical reaction;they are only rearranged

y Antoine Lavoisier Law of Conservation of Mass

mass is neither created nor destroyed in chemical orphysical changes

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http://www.chemteam.info/Gallery/Lavoisier.gif


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Chemical Equations:y How to balance an equation:

y Use coefficients a # placed in the front of a chemicalsymbol or formula

y Example: 2CO - 2 carbon monoxide molecules


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Chemical Equations:y Atoms must be counted to balance an equation

y Multiply the subscript of each element with the

coefficient

y Example: 2H2Oy 4 hydrogen atoms, 2 oxygen atoms

y

Only coefficients are changed

http://www.mikeblaber.org/oldwine/chm1045/notes/Stoich/Equation/coeff.gif


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Quick Quiz:

yWhat is the difference between a reactant and a

product?

yWhat is the difference between the formula CO andthe symbol Co?


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Reference:

Documents

Chemical Formulas & Equations Ch 14.2 8th