CHEMICAL REACTIONS Chapter 8

I. Forming New Substances A. chemical reactions 1. process where substances change into new substances (a chemical change) 2. new substances properties differ from those of the original substances 3. examples: leaves changing color, burning, rusting, souring, tarnishing, digesting

B. Signs of Chemical Reactions 1. formation of a gas (bubbles form) 2. energy change (may be given off in the form of light, heat, electricity) 3. color change (ex: bleach, leaves) 4. precipitate formation (solid substance formed in a solution) 5. change of properties (most imp. sign) NOTE: 1-4 above do not guarantee a reaction occurred Remember: A phase change is NOT a chemical reaction/change I. Forming New Substances …continued

C. Chemical Bonds 1. force that holds atoms together 2. original bonds must break & new bonds form in a chemical reaction 3. step 1 – chemical bonds break due to constantly moving molecules bumping into ea. other 4. step 2 – atoms rearrange (elements bond w/ other elements, etc.) 5. step 3 – new bonds form (makes new substances w/ new properties) I. Forming New Substances …continued

II. Chemical Formulas A. represents a substance B. uses chemical symbols & # C. shows how many atoms of each element are present in a molecule D. subscript - # written after & below a symbol showing how many atoms of that element there are (a “1” is not written it is understood)

E. ( ) are used if more than 1 polyatomic ion is present F. example: barium iodide = BaI 2 1 barium atom 2 iodine atoms atoms are in a 1:2 ratio aluminum carbonate=Al 2 (CO 3 ) 3 2 aluminum 3 carbon 9 oxygen G. practice reading formulas (worksheet) II. Chemical Formulas

III. Covalent Cmpds. (naming & formulas) A. usu. 2 nonmetals B. prefixes are used in naming to tell # of atoms present C. MUST know prefixes! mono- is not used with 1 st element named D. ex: carbon dioxide there is 1 carbon atom – (no mono- w/ 1 st name) there are 2 oxygen atoms (di- means 2) formula is CO 2

E. when naming: 1. use prefix, unless only 1, and name 1 st element 2. use prefix, name 2 nd element, and add –ide if only 2 elements are present III. Covalent Cmpds. (naming & …continued formulas)

IV. Ionic Cmpds. (naming & formulas) A. usu. a metal and nonmetal B. combines ions C. charges must balance out and = 0 D. overall charge of compound is neutral (0)

E. example: magnesium = +2 chloride = -1 it takes 2 chlorides to balance out 1 magnesium ( ) so the formula is MgCl 2 (1 magnesium & 2 chlorides) F. ‘criss-cross’ method G. To name – just name the (+) ion 1 st, then name the (-) ion and add –ide if a single element IV. Ionic Cmpds. (naming & …continued formulas)

V. Chemical Equations A. represents a chemical reaction B. shows: 1. what changes take place 2. relative amounts of the various substances involved in the reaction

C. set-up: 1. reactants starting substances on left side of equation 2. products ending substances formed as a result of the chemical reaction on right side of chemical equation V. Chemical Equations …continued

3. arrow means yield between the reactants & products treated as an equal sign 4. abbreviations used to id. substances’ phases (g)=gas, (l)=liquid, (cr)=solid, (aq)=aqueous V. Chemical Equations …continued

D. must be balanced 1. have the same kind & # of atoms on each side due to Law of Conservation of Mass 2. coefficients are used to balance (NOT subscripts) 3. there should be an = # of atoms for each element on both sides V. Chemical Equations …continued

E. steps: 1. write correct formulas for each substance 2. start at the front & go through the equation making sure the # of atoms/elements are the same – use coefficients to adjust V. Chemical Equations …continued

3. example: hydrogen + oxygen → water H 2 + O 2 → H 2 O (don’t forget diatomic molecules) 2 hydrogen → 2 hydrogen 2 oxygen → 1 oxygen (must be adjusted) use a 2 in front of water H 2 + O 2 → 2H 2 O (this makes hydrogen not balanced 2 hydrogen → 4 hydrogen) Use a 2 in front of hydrogen 2H 2 ­ + O 2 → 2H 2 O BALANCED!!

1. copper + water → copper II oxide + hydrogen 2. aluminum nitrate + sodium hydroxide → aluminum hydroxide + sodium nitrate 3. potassium nitrate → potassium nitrite + oxygen 4. iron + sulfuric acid → iron III sulfate + hydrogen 5. oxygen + carbon disulfide → carbon dioxide + sulfur dioxide 6. copper + chlorine → copper II chloride 7. magnesium + nitrogen → trimagnesium dinitride 8. When copper II carbonate is heated, it forms copper II oxide and carbon dioxide gas. 9. Sodium reacts with water to produce sodium hydroxide and hydrogen gas. 10. Copper combines with sulfur to form copper I sulfide. 11. Silver nitrate reacts with sulfuric acid to produce silver sulfate and nitric acid. 12. Ethane, C2H6, a compound of natural gas, burns in oxygen to produce carbon dioxide and water. V. Practice