# Chpt3 - Chapter 3 Stoichiometry Calculations with Chemical...

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Chapter 3 Stoichiometry: Calculations with Chemical Formulas and Equations

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Stoichiometry Stoichiometry is the area of study that examines the quantities of substances consumed and produced in a chemical reaction. Built on an understanding of atomic masses, chemical formulas, and the law of conservation of mass. The changes that occur in a chemical reaction only rearrange atoms, atoms are not created or destroyed.
Chemical Equations Concise representations of chemical reactions The “+” is read as “reacts with” The is read as “to produce” To the left of the arrow are reactants and to the right of the arrow are products . CH 4 ( g ) + 2 O 2 ( g ) CO 2 ( g ) + 2 H 2 O ( g )

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The states of the chemicals are written in parentheses to the right of each compound. (e.g. s, l, g, aq ) Coefficients are inserted to balance the equation. Temperature and pressure conditions are sometimes given. CH 4 ( g ) + 2 O 2 ( g ) CO 2 ( g ) + 2 H 2 O ( g ) Chemical Equations
Subscripts and Coefficients Give Different Information Subscripts tell the number of atoms of each element in a molecule Coefficients tell the number of molecules

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Start by writing the formulas of the reactants and products. Subscripts should never be changed in balancing an equation. Coefficients are inserted to balance the number of each type of atom in the equation. Start by balancing the elements that occur in the least number of chemical formulas, then balance the other elements. Balancing Chemical Equations C 8 H 18 ( l ) + O 2 ( g ) CO 2 ( g ) + H 2 O ( g )
Combination Reactions Examples: N 2 ( g ) + 3 H 2 ( g ) → 2 NH 3 ( g ) C 3 H 6 ( g ) + Br 2 ( l ) → C 3 H 6 Br 2 ( l ) 2 Mg ( s ) + O 2 ( g ) → 2 MgO ( s ) Two or more substances react to form one product

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2 Mg ( s ) + O 2 ( g ) → 2 MgO ( s )
Decomposition Reactions Examples: CaCO 3 ( s ) → CaO ( s ) + CO 2 ( g ) 2 KClO 3 ( s ) →

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