Chemical Equations Reactions Chemistry A Chemical Reactions You

Chemical Equations & Reactions Chemistry A

Chemical Reactions You should be able to ØClassify reactions by type. ØWrite a balanced molecular equation, complete ionic equation, and a net ionic equation. 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

Chemical Reaction A process in which at least one new substance is produced as a result of chemical change.

A Chemical Reaction Reactants Products

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

Writing a Chemical Equation Chemical symbols give a “before-and-after” picture of a chemical reaction Reactants Mg. O + Products C magnesium oxide reacts with carbon CO to form + Mg carbon monoxide and magnesium

Learning Check E 3 12 oz of dough, 4 oz mushrooms, 12 slices pepperoni, 8 oz cheese and 5 oz tomato sauce are used to make a pizza. Write a recipe in words for putting together a pizza. How would you write the recipe as an equation?

Solution E 3 Example: Combine 12 oz dough + 4 oz mushrooms + 12 slices pepperoni + 8 oz cheese + 5 oz tomato sauce and heat 30 minutes at 350°C to produce 1 pizza 12 oz dough + 4 oz mshrm + 12 pep + 8 oz chse 1 pizza + 5 oz tom sauce

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 100% Kotz web Chemical Factory 100% 20% 80%

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.

Balancing Chemical Equations Other examples NO(g) + O 2(g) NO 2(g) is it balanced? Is this balanced? NO(g) + O(g) NO 2(g) Is this OK? Is this balanced? NO(g) + ½ O 2(g) NO 2(g) Is this OK?

Balancing Chemical Equations An important point to remember 2 NO(g) + O 2(g) 2 NO 2(g) The 2 to the left of NO(g) and NO 2(g) refers to the number of molecules present in the balanced equation. It is a “multiplier” for every atom in the molecule. The subscript 2 in O 2 (g) and NO 2(g) refers to the number of atoms of this type that are present in each molecules (or ionic compound).

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 + C(s) + carbon O 2(g) CO 2(g) oxygen carbon dioxide Reactants 1 carbon atom 2 oxygen atoms Product 1 carbon atom 2 oxygen atoms catalyst – speeds up reaction + 2 H 2(g) + hydrogen Pt O 2(g) Pt oxygen Reactants 2 hydrogen atoms 4 2 oxygen atoms 2 H 2 O (l) water Product 2 hydrogen atoms 4 1 oxygen atoms 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

Types of Chemical Reactions Synthesis (Combination) reaction A + B AB AB A + B Decomposition reaction ASingle-replacement A + BC AC + B reaction element BDouble-replacement reaction Polymerization Ause activity series to predict Bdriving force…water, gas, or precipitate element compound HX + BOH BX + HOH acid Combustion reaction (of a hydrocarbon) compound AB + CD AD + CB compound Neutralization reaction compound base salt water CH + O 2 CO 2 + H 2 O Polymer = monomer + …

Types of Chemical Reactions Synthesis (Combination) reaction Decomposition reaction ASingle-replacement reaction BDouble-replacement reaction Neutralization reaction Combustion reaction (of a hydrocarbon) Polymerization Ause activity series to predict Bdriving force…water, gas, or precipitate A + B AB AB A + BC AC + B AB + CD AD + CB HX + BOH BX + HOH CH + O 2 CO 2 + H 2 O Polymer = monomer + …

Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Na Cl 2 Cl Cl 2 Na. Cl Na General form: A element or compound + B element or compound AB compound

Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl 2 Na. Cl Cl Na+ Cl - Cl Cl - Na+ Na General form: A element or compound + B element or compound AB compound

Decomposition Reaction Decomposition reaction 2 H 2 O 2 H 2 + O 2 H O H + H O H General form: AB compound A + B two or more elements or compounds

Single and Double Replacement Reactions Single-replacement reaction Mg + Cu. SO 4 General form: A + BC Mg. SO 4 AC + + Cu B Double-replacement reaction Ca. CO 3 + General form: AB + 2 HCl Ca. Cl 2 + H 2 CO 3 CD AD + CB

Double Replacement Reaction K 2 CO 3 (aq) Potassium carbonate + Ba. Cl 2 (aq) Barium chloride 2 KCl (aq) Potassium chloride + Ba. CO 3 (s) Barium carbonate

Synthesis Reactions Photosynthesis 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + Formation of water 2 H 2 + O 2 2 H 2 O Formation of salt 2 Na + Cl 2 2 Na. Cl General Form A + B C 6 O 2

Decomposition Reactions Hydrogen Peroxide 2 H 2 O 2 2 H 2 O + 2 H 2 + O 2 Electrolysis of water 2 H 2 O electricity O 2 Nitrogen triiodide 2 NI 3 N 2 + 3 I 2 General Form AB A + B