Chap 8: Chemical Equation and Reaction

8.1 Describing Chemical Reactions 1.What is chemical reaction? 2. What are the evidences that a chemical reaction is taking place?

Physical change vs. Chemical change Chemical ChangePhysical Change

Physical ChangesChemical Changes Aluminum foil is cut in half.Milk goes sour. Clay is molded into a new shape.Jewelry tarnishes. Butter melts on warm toast.Bread becomes toast. Water evaporates from the surface of the ocean. Rust forms on a nail left outside. A juice box in the freezer freezes.Gasoline is ignited. Rubbing alcohol evaporates on your hand. Hydrogen peroxide bubbles in a cut. Food scraps are turned into compost in a compost pile. A match is lit. You take an antacid to settle your stomach. Your body digests food. You fry an egg.

I. Describing Chemical Change Word equation? –Reactants  Products –Read as: –Ex: Iron + oxygen  Iron(III)oxide –Read as: –ex: hydrogen peroxide  water + oxygen

Chemical Equation: –Skeleton equation- –Physical states can be identified as- (s) (l) (g) (aq) –Additional symbols: see Table 8-2 catalyst –Ex. Match maker

Equation can show physical state and reaction conditions H 2 (g) + O 2 (g) H 2 O (l) H 2 + O 2 balloon rxn

When solid aluminum oxide and hydrogen gas are heated, molten aluminum and water vapor form. –Write a word equation for the above reaction –Write an unbalanced formula using all appropriate symbols (skeleton equation) Aluminum =Oxygen = Aluminum Oxide =

Check your understanding! Describe how both chemical and physical changes occur in your mouth when you chew food How might you use a magnet to show that a completely rusted iron name has undergone a chemical change?

Magnesium oxide forms from magnesium metal and oxygen gas. Write a word equation and unbalanced formula equation. Include all appropriate notations.

VII. Balancing Chemical Equations A. Chemical equations must be balanced due to the Law of Conservation of _____. (_________). Reactants are written on the left of the arrow, ________ are written to the right of the arrow. ____________  ____________ B. Equations are balanced by changing __________, not by changing __________. For now all equations will be balanced using ______ numbers. C. Certain elements will are found as _______ molecules in nature. In a chemical equation, they will be written in this form. The elements are easily remembered by learning the name of the German guy: Mr. __________. The seven diatomic molecules are:___, ___, ___, ___, ___, ___, and ___. Lavoisier

Balancing Chemical Equations

Mr. HOFBrINCl Memorize: H 2, N 2, F 2, O 2, I 2, Cl 2, Br 2 O, HuCklBerryFIN

D. Coefficients: Small, ______ numbers placed before the chemical formula. They are multiplied by each atom in the compound. E. Law of Conservation of Mass: Matter cannot be _______ nor _________, so reactions must be _________. F. Tips for balancing equations: 1. Number of atoms of _________ must equal number of atoms of ________. 2. Coefficients are whole numbers written at the _________ of the substances. 3. All atoms are __________ by the coefficients. 4. Subscripts are ______ changed. 5. Keep polyatomic ions together as a _______ if unchanged from reactants to products. 6. Balance single elements _____. 7. Use the even/odd rule. 8. If an element is in _______ compounds, balance that element last.

Example: Lighting a match: 1. Observations: 2. Word Equation: 3. Skeleton Equation: P 4 + ________  _______+________ 4. Balanced Equation: phosphorus + potassium chlorate  potassium chloride + diphosphorus pentoxide

Balancing Chemical Eq’n: –each side of the eq’n has the same number of atoms ex: write the word eq’n for making a bike: ______ + _______ + _________ + _____  bicycle write a skeleton eq’n for it using symbols _____ + _____ + _____ + _____  _______ use coefficients which are numbers in front of the symbols to balance the equation.

Ex.1: carbon reacts with oxygen gas to produce carbon dioxide: already balanced- 1: 1: 1 Ex.2: hydrogen gas reacts with oxygen gas to produce water: balanced ratio- 2: 1: 2 C+O2O2  CO 2 C O H2H2 +O2O2  H2OH2O H O

fig. 8.4 p. 249 Interpreting a Chemical Reaction How many molecules are on each side? How many moles? What is total mass of reactants? Of products? Is the reaction balanced?

Balance the following equations ZnS + O 2  ZnO + SO 2 Fe 2 O 3 + CO  Fe + CO 2 AgNO 3 + AlCl 3  AgCl + Al(NO) 3

1.___NaClO 3  ___NaCl + ___O 2 2.___Fe 3 O 4 + ___H 2  ___Fe + ___H 2 O Sample Problems: 1. Hydrogen + oxygen  water 2.Zinc + hydrochloric acid  zinc chloride + hydrogen 3. Copper + silver nitrate  cupric nitrate + silver 4. Ferric hydroxide  iron (III) oxide + water

5. Ethane (C 2 H 6 ) + oxygen  carbon dioxide + water 6. Calcium + water  calcium hydroxide + hydrogen 7. Potassium + sulfuric acid  potassium sulfate + hydrogen 8. Calcium nitrate + aluminum sulfite  calcium sulfite + aluminum nitrate 9. Phosphoric acid is formed when crystalline diphosphorus pentoxide is dissolved in water.

10. When rust (ferric oxide) is dissolved in hydrochloric acid, it dissolves forming aqueous ferric chloride and water. 11. Benzene, C 6 H 6, is an organic solvent used to dissolve many organic compounds. Write an equation for the combustion of liquid benzene (carbon dioxide and water are formed). 12. When a solution of aqueous plumbic nitrate and aqueous barium hydroxide are mixed, solid plumbic hydroxide and aqueous barium nitrate are formed.

Reaction Types

Combination (Synthesis) Reactions Two or more substances combine to form a new compound.  Reaction of elements with oxygen and sulfur  Reactions of metals with Halogens  Synthesis Reactions with Oxides  There are others not covered here!

Decomposition Reactions A single compound undergoes a reaction that produces two or more simpler substances Decomposition of: Binary compounds H 2 O( l )  2H 2 (g) + O 2 (g) Metal carbonates CaCO 3 (s)  CaO(s) + CO 2 (g) Metal hydroxides Ca(OH) 2 (s)  CaO(s) + H 2 O(g) Metal chlorates 2KClO 3 (s)  2KCl(s) + 3O 2 (g) Oxyacids H 2 CO 3 (aq)  CO 2 (g) + H 2 O( l )

Classify the following reactions as synthesis or decomposition: H 2 + Br 2 2HBr Synthesis Al 2 (CO 3 ) 3 Al 2 O 3 + 3CO 2 Decomposition 4 Al + 3C Al 4 C 3 Synthesis

Combustion Reactions A substance combines with oxygen, releasing a large amount of energy in the form of light and heat. Reactive elements combine with oxygen (This is also a synthesis reaction) The burning of natural gas, wood, gasoline

Single Replacement Reactions Replacement of:  Metals by another metal  Hydrogen in water by a metal  Hydrogen in an acid by a metal  Halogens by more active halogens

The Activity Series of the Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold  Metals can replace other metals provided that they are above the metal that they are trying to replace  Metals above hydrogen can replace hydrogen in acids.  Metals from sodium upward can replace hydrogen in water

The Activity Series of the Halogens Fluorine Chlorine Bromine Iodine Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace.

Double Replacement Reactions The ions of two compounds exchange places in an aqueous solution to form two new compounds. precipitateinsoluble gas molecular compound One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of solution, or a molecular compound, usually water.

Single or Double Replacement? 2Al + 3H 2 SO 4 Al 2 (SO 4 ) 3 + 3H 2 Single Na 2 SO 4 + 2AgNO 3 Ag 2 SO 4 + 2NaNO 3 Double 3C + Fe 2 O 3 2Fe + 3CO Single

Examples: Determine the product and reaction type H 2 + O 2  H 2 O  Zn + H 2 SO 4  HgO  KBr +Cl 2  AgNO 3 + NaCl  Mg(OH) 2 + H 2 SO 3 