Presentation is loading. Please wait.

Presentation is loading. Please wait.

Chemical Equations & Reactions. Describing a Chemical Reaction Indications of a Chemical Reaction –Evolution of heat, light, and/or sound –Production.

Similar presentations


Presentation on theme: "Chemical Equations & Reactions. Describing a Chemical Reaction Indications of a Chemical Reaction –Evolution of heat, light, and/or sound –Production."— Presentation transcript:

1 Chemical Equations & Reactions

2 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

3 Chemical Equations reactantsproducts 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 numbers in the front are called stoichiometric coefficients stoichiometric coefficients. The letters (s), (g), and (l) are the physical states of compounds.

4 Chemical Equations This equation means: 4 Al(s) + 3 O 2 (g) 2 Al 2 O 3 (s) 4 Al atoms + 3 O 2 molecules yield 2 molecules of Al 2 O 3 4 Al moles + 3 O 2 moles yield 2 moles of Al 2 O 3 or

5 Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (reactants), the amount of matter in a system does not change. Law of Conservation of Matter The Law of Conservation of Matter

6 Chemical Equations conservation of matter Because of the principle of the conservation of matter, equation must be balanced An equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788

7 Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: change in colorchange in odorproduction of new gases or vapor input or release of energy difficult to reverse release input

8 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. Reactants→Products

9 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 carbon dioxide + water Reactant Product

10 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 O 2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

11 Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s)(s) (l)(l) (aq) (g)(g)

12 Additional Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product 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 Temperature at which reaction is carried out, in this case 0 o C Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction 2 atm pressure 0 o C MnO 2 

13 Showing Phases in Chemical Equations Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(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) H 2 O(s) H 2 O(l) H 2 O(g)

14 Types of Chemical Reactions Synthesis (Combination) reaction Decomposition reaction A Single-replacement reaction B Double-replacement reaction Acid base reaction Combustion reaction (of a hydrocarbon) A + B  AB AB  A + B A + BC  AC + B AB + CD  AD + CB HX + BOH  BX + HOH CH + O 2  CO 2 + H 2 O A use activity series to predict B driving force…water, gas, or precipitate

15 Synthesis Reaction Direct combination reaction (Synthesis) General form: A + B  AB element orelement or compoundcompound Na + Cl - Na ClNa Cl Na + Cl - 2 Na + Cl 2  2 NaCl

16 H H H H Decomposition Reaction H H H H O Decomposition reaction 2 H 2 O 2 H 2 O2O2 General form: ABAB compoundtwo or more elements or compounds OO O H H H H Decomposition Reaction H H H H O Decomposition reaction 2 H 2 O 2 H 2 O2O2 General form: ABAB compoundtwo or more elements or compounds OO O

17 Single and Double Replacement Reactions Double-replacement reaction CaCO HCl  CaCl 2 + H 2 CO 3 General form: AB + CD  AD + CB Single-replacement reaction Mg + CuSO 4  MgSO 4 + Cu General form: A + BC  AC + B

18 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 P 4 (s) + 5O 2 (g)  P 4 O 10 (s) (This is also a synthesis reaction) The burning of natural gas, wood, gasoline C 3 H 8 (g) + 5O 2 (g)  3CO 2 (g) + 4H 2 O(g)

19 Unbalanced and Balanced Equations Cl H H H HH H H H 2 + Cl 2  HCl (unbalanced) H 2 + Cl 2  2 HCl (balanced) reactants products 2 H Cl H

20 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 O 2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

21 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 NaOH + H 2 2 Na + 2 H 2 O  2 NaOH + H 2

22 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.

23 1) Write a word equation for the reaction. Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 2) Write the correct formulas for all reactants and products. 3) Determine the coefficients that make the equation balance. chlorine + sodium bromide  bromine + sodium chloride Cl 2 + NaBr  Br 2 + NaCl Cl NaBr  Br NaCl

24 1) Write a word equation for the reaction. 2) Write the correct formulas for all reactants and products. 3) Determine the coefficients that make the equation balance. aluminum sulfate + calcium chloride  calcium sulfate + aluminum chloride Al 2 (SO 4 ) 3 + CaCl 2  CaSO 4 + AlCl 3 Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. Al 2 (SO 4 ) CaCl 2  3 CaSO AlCl 3

25 CH O 2  CO H 2 O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms


Download ppt "Chemical Equations & Reactions. Describing a Chemical Reaction Indications of a Chemical Reaction –Evolution of heat, light, and/or sound –Production."

Similar presentations


Ads by Google