Chapter 6 Chemical Reactions and Equations

Chemical Reactions The process in which 1 or more substances are converted into new substances The process in which 1 or more substances are converted into new substances Existing bonds are broken, atoms are rearranged, and new bonds are formed Existing bonds are broken, atoms are rearranged, and new bonds are formed Reactant: substance that enters a reaction Reactant: substance that enters a reaction Product: substance produced Product: substance produced

Chemical Equations represent chemical reactions Word Equations: gives names of reactants and products Word Equations: gives names of reactants and products Calcium + oxygen  calcium oxide Formula Equations: uses chemical symbols and formulas instead of names Formula Equations: uses chemical symbols and formulas instead of names Ca + O 2  CaO

Balancing Chemical Equations The law of conservation of matter state that matter cannot be created or destroyed The law of conservation of matter state that matter cannot be created or destroyed Number of atoms of each element must be the same before and after a reaction Number of atoms of each element must be the same before and after a reaction When this occurs, the equation is balanced. When this occurs, the equation is balanced.

Balancing Chemical Equations When balancing… When balancing… Do not change subscripts Do not change subscripts Changing subscripts changes the compounds Changing subscripts changes the compounds In balancing equations, coefficients are added in front of entire compounds In balancing equations, coefficients are added in front of entire compounds The coefficients then apply to the entire compound The coefficients then apply to the entire compound Coefficients mean multiples of that compound. Coefficients mean multiples of that compound.

Hints on Balancing Equations Balance equations in the following order: Balance equations in the following order: Polyatomic ions that show up on both sides Polyatomic ions that show up on both sides Metallic elements Metallic elements Nonmetals other than Oxygen and Hydrogen Nonmetals other than Oxygen and Hydrogen Hydrogen and oxygen Hydrogen and oxygen

Writing Balanced Equations Write the balanced chemical equation for the following reaction: Write the balanced chemical equation for the following reaction: -Lithium hydroxide is reacted with sulfuric acid to produce lithium sulfate and water.

Complete chemical equations denote state of matter (s) = solid (s) = solid (l) = liquid (l) = liquid (g) = gas (g) = gas (aq) = aqueous solution; the compound is dissolved in water (aq) = aqueous solution; the compound is dissolved in water Ca(s) + O 2 (g)  CaO(s)

Classifying Chemical Reactions Direct Combination/Synthesis: Direct Combination/Synthesis: 2 or more reactions come together to make a single product 2 or more reactions come together to make a single product A + B  AB Na(s) + Cl 2 (g)  NaCl(s)

Decomposition Reactions: Decomposition Reactions: A large reactant breaks down to form 2 or more simpler substances A large reactant breaks down to form 2 or more simpler substances AB  A + B CaCO 3 (s)  CaO(s) + CO 2 (g)

Single Replacement Reactions: Single Replacement Reactions: One atom replaces another in an ionic compound One atom replaces another in an ionic compound A + BX  AX + B Mg(s) + CuSO 4 (aq)  MgSO 4 (aq) + Cu(s) Depends on the activity of the atoms. A more active atom replaces a less active atom. Depends on the activity of the atoms. A more active atom replaces a less active atom. Pg. 295: Activity series of metals Pg. 295: Activity series of metals

Double Replacement Reactions: Double Replacement Reactions: 2 ionic compounds switch anions 2 ionic compounds switch anions AX + BY  AY + BX CaCO 3 + 2HCl  CaCl 2 + H 2 CO 3

Combustion Combustion When something is burned, oxygen (O 2 ) is added and the compound is broken up. When something is burned, oxygen (O 2 ) is added and the compound is broken up. H 2 + O 2  H 2 O CH 4 + O 2  CO 2 + H 2 O Hydrocarbons (molecules made of just carbon, hydrogen, and oxygen combust to make carbon dioxide and water) Hydrocarbons (molecules made of just carbon, hydrogen, and oxygen combust to make carbon dioxide and water)

Writing Chemical Equations 1. Write out the reactants 1. Write out the reactants 2. Determine what type of reaction 2. Determine what type of reaction 3. Write out the products in words 3. Write out the products in words 4. Write out products using the chemical formula 4. Write out products using the chemical formula 5. Balance the equation by adding coefficients in front of the compounds as needed 5. Balance the equation by adding coefficients in front of the compounds as needed