Chemical Reactions

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Chemical Reactions. Chapter 10. Chemical Reactions and Equations: Basic Concepts. Topic 8. Recognizing Chemical Reactions. When a substance undergoes a chemical change, it takes part in a chemical reaction. After it reacts, it no longer has the same chemical identity. - PowerPoint PPT Presentation

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Chemical Reactions

Chemical ReactionsChapter 101When a substance undergoes a chemical change, it takes part in a chemical reaction.Recognizing Chemical ReactionsChemical Reactions and Equations: Basic ConceptsAfter it reacts, it no longer has the same chemical identity.Topic 8

2Writing Chemical EquationsA substance that undergoes a reaction is called a reactant.When reactants undergo a chemical change, each new substance formed is called a product.

Chemical Reactions and Equations: Basic ConceptsTopic 83Word EquationsThe simplest way to represent a reaction is by using words to describe all the reactants and products, with an arrow placed between them to represent change.Reactants are placed to the left of the arrow, and products are placed to the right.Plus signs are used to separate reactants and also to separate products.

Chemical Reactions and Equations: Basic ConceptsTopic 84Chemical EquationsWord equations describe reactants and products, but they are long and awkward and do not adequately identify the substances involved.Word equations can be converted into chemical equations by substituting chemical formulas for the names of compounds and elements.Chemical Reactions and Equations: Basic ConceptsTopic 85Chemical EquationsThe equation for the reaction of vinegar and baking soda can be written using the chemical formulas of the reactants and products.By examining a chemical equation, you can determine exactly what elements make up the substances that react and form.

Chemical Reactions and Equations: Basic ConceptsTopic 86Chemical EquationsIt may also be important to know the physical state of each reactant and product.How can we indicate the bubbles we see during this reaction are CO2?Symbols in the parentheses are put after formulas to indicate the state of the substance.Solids, liquids, gases, and water (aqueous) solutions are indicated by the symbols (s), (l), (g), and (aq).Chemical Reactions and Equations: Basic ConceptsTopic 87Chemical EquationsThe following equation shows these symbols added to the equation for the reaction of vinegar and baking soda.

Chemical Reactions and Equations: Basic ConceptsTopic 88Balancing Chemical EquationsThe mass of the products is always the same as the mass of the reactants that react to form them.The law of conservation of mass summarizes these findings. Matter is neither created nor destroyed during a chemical reaction.Chemical Reactions and Equations: Basic ConceptsTopic 89Balancing Chemical EquationsRemember that atoms dont change in a chemical reaction; they just rearrange.The number and kinds of atoms present in the reactants of a chemical reaction are the same as those present in the products.When stated this way, it becomes the law of conservation of atoms.Chemical Reactions and Equations: Basic ConceptsTopic 810Balancing Chemical EquationsFor a chemical equation to accurately represent a reaction, the same number of each kind of atom must be on the left side of the arrow as are on the right side.If an equation follows the law of conservation of atoms, it is said to be balanced.Chemical Reactions and Equations: Basic ConceptsTopic 8

Click box to view movie clip.11Balancing Chemical EquationsThe easiest way to count atoms is to practicefirst with a simple reaction and then with some that are more complex.For example, consider the equation that represents breaking down carbonic acid into water and carbon dioxide.

Chemical Reactions and Equations: Basic ConceptsTopic 812Balancing Chemical EquationsBecause a subscript after the symbol for an element represents how many atoms of that element are found in a compound, you can see that there are two hydrogen, one carbon, and three oxygen. All of the atoms in the reactants are the same as those found in the products.Chemical Reactions and Equations: Basic ConceptsTopic 813Balancing an EquationThe balanced equation tells us that when sodium hydroxide and carbon dioxide react, two units of sodium hydroxide react with each molecule of carbon dioxide to form one unit of sodium carbonate and one molecule of water.Chemical Reactions and Equations: Basic ConceptsTopic 8

14Major Classes of ReactionsIn one type of reaction, two substanceseither elements or compoundscombine to form a compound.Whenever two or more substances combine to form a single product, the reaction is called a synthesis reaction.

Chemical Reactions and Equations: Basic ConceptsTopic 815A Synthesis ReactionWhen iron rusts, iron metal and oxygen gas combine to form one new substance, iron(III) oxide.The balanced equation for this synthesis reaction shows that there is more than one reactant but only one product.

Chemical Reactions and Equations: Basic ConceptsTopic 8

16A Synthesis Reaction

Chemical Reactions and Equations: Basic ConceptsTopic 817Major Classes of ReactionsIn a decomposition reaction, a compound breaks down into two or more simpler substances.The compound may break down into individual elements, such as when mercury(II) oxide decomposes into mercury and oxygen.Chemical Reactions and Equations: Basic ConceptsTopic 8

18A Decomposition ReactionWhen ammonium nitrate is heated to a high temperature, it explosively breaks down into dinitrogen monoxide and water.The decomposition reaction taking place is represented by a balanced equation that shows one reactant and more than one product.

Chemical Reactions and Equations: Basic ConceptsTopic 819A Decomposition Reaction

Chemical Reactions and Equations: Basic ConceptsTopic 820Major Classes of ReactionsIn a single-displacement reaction, one element takes the place of another in a compound.The element can replace the first part of a compound, or it can replace the last part of a compound.

Chemical Reactions and Equations: Basic ConceptsTopic 8

21Single DisplacementIf an iron nail is placed into an aqueous solution of copper(II) sulfate, the iron displaces the copper ions in solution, and copper metal forms on the nail.

Chemical Reactions and Equations: Basic ConceptsTopic 822Single Displacement

Chemical Reactions and Equations: Basic ConceptsTopic 823Major Classes of ReactionsIn double-displacement reactions, the positive portions of two ionic compounds are interchanged.For a double-displacement reaction to take place, at least one of the products must be a precipitate or water.

Chemical Reactions and Equations: Basic ConceptsTopic 8

24Double DisplacementWhen clear aqueous solutions of lead(II) nitrate and potassium iodine are mixed, a double-displacement reaction takes place and a yellow solid appears in the mixture.This solid is lead(II) iodine, and it precipitates out because it is insoluble in water, unlike the two reactants and the other product.Chemical Reactions and Equations: Basic ConceptsTopic 8

25Double Displacement

Chemical Reactions and Equations: Basic ConceptsTopic 826CombustionWhen welding is done with an acetylene torch, acetylene combines with oxygen to form carbon dioxide and water.This combustion reaction is exothermic, and enough energy is released to melt metal.

Chemical Reactions and Equations: Basic ConceptsTopic 8

27Combustion

Chemical Reactions and Equations: Basic ConceptsTopic 828Basic Assessment Questionsdecomposition; already balancedAnswer 3bQuestion 3b

Topic 829Basic Assessment Questionssynthesis;Answer 3aQuestion 3a

Topic 830