Chemical Equations Reactions http www unit 5 orgchemistryEquations
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Chemical Equations & Reactions http: //www. unit 5. org/chemistry/Equations. html
Lecture Outline – Chemical Equations & Reactions student notes outline textbook questions Lecture Outline – Chemical Equations & Reactions textbook questions Keys text http: //www. unit 5. org/chemistry/Equations. html
Chemical Reactions You should be able to ØClassify reactions by type. ØWrite a balanced molecular equation, complete ionic equation, and a net ionic equation. ØBalance oxidation-reduction reactions. ØPredict if a precipitate will form using the solubility rules. ØPredict products of reactions given the chemical names of the reactants.
Organize Your Thoughts Chemical reactions Chemical equations • Balancing equations • Predicting products from reactants Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175 Chemical equations • Synthesis • Decomposition • Single replacement • Double replacement • Combustion
Describing a Chemical Reaction Indications of a Chemical Reaction – Evolution of heat, light, and/or sound – Production of a gas – Formation of a precipitate – Color change
Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: release input change in color change in odor production of new gases or vapor input or release of energy difficult to reverse
Chemical Equations aluminum oxide Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O 2(g) 2 Al 2 O 3(s) The letters (s), (g), and (l) are the physical states of compounds. The numbers in the front are called stoichiometric coefficients
Chemical Equations 4 Al(s) + 3 O 2(g) 2 Al 2 O 3(s) aluminum oxide sandpaper 4 g Al + 3 g O 2 yield 2 g Al 2 O 3 This equation means: 4 Al atoms + 3 O 2 molecules yield 2 molecules of Al 2 O 3 or 4 Al moles + 3 O 2 moles yield 2 moles of Al 2 O 3 4 mol Al@27 g/mol 3 mol O 2@32 g/mol 108 g + 96 g 2 mol Al 2 O 3@102 g/mol = 204 g
Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. The Law of Conservation of Matter Kotz web
Chemical Equations Because of the principle of the conservation of matter, matter An equation must be balanced It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788
Characteristics of Chemical Equations • The equation must represent known facts. • The equation must contain the correct formulas for the reactants and products. • The law of conservation of mass must be satisfied.
Chemical Equations • Reactants – the substances that exist before a chemical change (or reaction) takes place. • Products – the new substance(s) that are formed during the chemical changes. • CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS PRODUCTS
Word Equations • A WORD EQUATION describes chemical change using the names of the reactants and products. Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen Reactant CH 4 + 2 O 2 carbon dioxide + water Product CO 2 + 2 H 2 O
Unbalanced and Balanced Equations H Cl Cl H H Cl H 2 + Cl 2 HCl (unbalanced) reactants H Cl 2 2 H H Cl Cl Cl H 2 + Cl 2 2 HCl (balanced) reactants products 1 1 Cl H Cl 2 2 products 2 2
Visualizing a Chemical Reaction 2 Na 10 mole Na ___ + Cl 2 5 mole Cl 2 ___ 2 Na. Cl 10 ? mole Na. Cl ___
Visualizing a Chemical Reaction 2 Na + Cl 2 2 Na. Cl
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 One molecule of hydrogen peroxide: Two H atoms and two O atoms
Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. 2 Na + H 2 O 2 Na. OH + H 2 2 Na + 2 H 2 O 2 Na. OH + H 2
Balancing Chemical Equations • Write a word equation for the reaction. • Write the correct formulas for all reactants and products. • Determine the coefficients that make the equation balance.
Guidelines for Balancing Chemical Equations ? 1) polyatomic ions first 2) even / odd (make all even) 3) 2 H-OH vs. H 2 O Mg(OH)2 4) single elements last Example: need 13 oxygen atoms “ ” Multiply by 13 O 2 = 13 2 3 X + 13 2 O 2 2 3 X + 6 X + 2 Y + Z O 2 2 Y + Z 13 O 2 4 Y + 2 Z 13 2
6 NH? 4 OH 2 (NH 4)3 PO 4 + 3 Mg(OH)2 Mg 3(PO 4)2 + ammonium phosphate magnesium hydroxide magnesium phosphate ammonium hydroxide NH 41+ OH 1 - Now you try… 2 Al. Cl 3 + 3 Li 2 CO 3 Al 2(CO 3)3 + 6 Li. Cl
Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 1) Write a word equation for the reaction. chlorine + sodium bromide bromine + sodium chloride 2) Write the correct formulas for all reactants and products. Cl 2 + Na. Br Br 2 + Na. Cl 3) Determine the coefficients that make the equation balance. Cl 2 + 2 Na. Br Br 2 + 2 Na. Cl
Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. 1) Write a word equation for the reaction. ? ? aluminum sulfate + calcium chloride calcium sulfate + aluminum chloride 2) Write the correct formulas for all reactants and products. Al 2(SO 4)3 + Ca. Cl 2 Ca. SO 4 + Al. Cl 3 3) Determine the coefficients that make the equation balance. Al 2(SO 4)3 + 3 Ca. Cl 2 3 Ca. SO 4 + 2 Al. Cl 3
CH 4 + 2 O 2 CO 2 + 2 H 2 O Reactants 1 C atom 4 H atoms 4 O atoms Products 1 C atom 4 H atoms 4 O atoms
Reactants Products catalyst – speeds up reaction 2 2 Unbalanced
Showing Phases in Chemical Equations H 2 O(s) H 2 O(l) H 2 O(g) Solid Phase – the substance is relatively rigid and has a definite volume and shape. Na. Cl(s) Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H 2 O(l) Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl 2(g)
Additional Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction (s) A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate (l) A reactant or product in the liquid state (aq) A reactant or product in an aqueous solution (dissolved in water) (g) A reactant or product in the gaseous state
Additional Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product D 2 atm pressure Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure 0 o. C Temperature at which reaction is carried out, in this case 0 o. C Mn. O 2 Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction
Solubility Ionic Equations Cover the answers, work the problem, then check the answer. 1. Dissolve ammonium nitrate: NH 4 NO 3 (s) ---> NH 4+1 (aq) + NO 3 -1 (aq) 2. Precipitate cupric hydroxide: Cu+2 (aq) + 2 OH-1 (aq) ---> Cu(OH)2 (s) 3. Dissolve chromium thiocyanate: 4. Precipitate lead arsenate: Cr(SCN)3 (s) ---> Cr+3 (aq) + 3 SCN-1 (aq) 3 Pb+2 (aq) + 2 As. O 4 -3 (aq) ---> Pb 3(As. O 4)2 (s) 5. Dissolve silicon permanganate: Si(Mn. O 4)4 (s) ---> Si+4 (aq) + 4 Mn. O 4 -1 (aq) 6. Precipitate zinc phosphate: 3 Zn+2 (aq) + 2 PO 4 -3 (aq) ---> Zn 3(PO 4)2 (s)
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