IIIIIIIVV A Balancing Act Chemical Reactions

Chemical Reactions Take Place… n Every minute of every day both in and around you n Examples:  Digestion  Photosynthesis  Car batteries-to start your car  Rust

Reactions: n One or more substances, the ___________ change into one or more new substances, the __________.  It is written as: - Reactants → Products  The arrow means - “yields” or “reacts to produce” reactants products

Explanation: n An explanation was proposed by _____________ who stated in his atomic theory that in a chemical reaction, the way in which atoms are joined together are changed. n As reactants are converted to new products, __________that hold atoms together are __________ and new ones are formed. Dalton bonds broken

Explanation: n Daltons atomic theory explains the ____________________________.  Which States: - In any physical or chemical change mass is neither created nor destroyed. - The atoms in the products are the same atoms that were in the reactants, they are just arranged differently. Law of Conservation of Mass

Explanation/Practice: n In a word equation, reactants are written on the ___________ and products are written on the ________. n Write the equation for…  Copper can be produced by heating copper (II) sulfide with oxygen. Sulfur dioxide is also produced.  Water is formed by the explosive reaction between hydrogen and oxygen left right

Answers n Copper(II)sulfide + Oxygen → Copper + Sulfer dioxide n Hydrogen + Oxygen → Water (Dihydrogen monoxide)

Meaning of Chemical Formula Chemical Symbol Meaning Composition H 2 O One molecule of water: Two H atoms and one O atom 2 H 2 O Two molecules of water: Four H atoms and two O atoms H 2 O 2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

Meaning of Chemical Formula n When a __________ is written after the chemical symbol for an element it indicates the___________________. n When a coefficient is written in front of an atom or molecule it indicates the ____________ of that atom or molecule that is present. n If there are subscripts in that atom/molecule they need to be ____________ by the coefficient. subscript number multiplied # of that element

Reactants  Products Unbalanced Timberlake, Chemistry 7 th Edition, page 164

Unbalanced and Balanced Equations Cl H H H HH H H H 2 + Cl 2  HCl (unbalanced) H 2 + Cl 2  2 HCl (balanced) reactants products 2 H Cl H Timberlake, Chemistry 7 th Edition, page 167

How do we go from Unbalanced to Balanced Equations? n You ____________ change the formula of your atom/ion/molecule! n This means you may not change the ___________ ! n Instead, you may put a coefficient __________ of your atom/ion/molecule to balance the number of atoms after you have ___________ it by the subscript MAY NOT subscript in front multiplied

CH O 2  CO H 2 O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms Timberlake, Chemistry 7 th Edition, page 167 Balanced!

Balancing Steps 1.Write the unbalanced equation. 2.Count atoms on each side. 3.Add coefficients as needed to make #s equal on both sides of the equation. Coefficient  subscript = # of atoms 4.Reduce coefficients to lowest possible ratio, if necessary. 5.Double check atom balance!!!

Helpful Tips n Balance one element at a time. n Update ALL atom counts after adding a coefficient. n If an element appears more than once per side, balance it last. n Balance polyatomic ions as single units.  “1 SO 4 ” instead of “1 S” and “4 O”

Al + CuCl 2  Cu + AlCl 3 Al Cu Cl  3  6   Balancing Example Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2  2  6

More Examples… P+O 2 →P 4 O 10 H 2 + O 2 → H 2 O BaCl 2 +H 2 SO 4 →BaSO 4 + HCl Cu+ AgNO 3 → Cu(NO 3 ) 2 + Ag CaCO 3 + HCl → CaCl 2 + H 2 CO