major classes of reactions if you can classify a reaction into one of five major categories by...
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Major Classes of Reactions
• If you can classify a reaction into one of five major categories by recognizing patterns that occur, you already know a lot about the reaction.
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Major Classes of Reactions
• In one type of reaction, two substances—either elements or compounds—combine 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 ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
A Synthesis Reaction
• When 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 ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
A Synthesis Reaction
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Major Classes of Reactions
• In 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 ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Major Classes of Reactions
• The products may be an element and a compound, such as when hydrogen peroxide decomposes into water and oxygen.
• The compound may break down into simpler compounds.
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
A Decomposition Reaction
• When 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 ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
A Decomposition Reaction
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Major Classes of Reactions
• In 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 ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Single Displacement
• If 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 ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Single Displacement
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Major Classes of Reactions• In 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, gas or water.
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Double Displacement
• When 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 ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Double Displacement
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Reactions in Aqueous Solutions
• Another example of a double-replacement reaction that produces a precipitate occurs when aqueous solutions of sodium chloride and silver nitrate are mixed to form a precipitate of solid silver chloride.
Chemical Reactions and Equations: Additional ConceptsChemical Reactions and Equations: Additional Concepts Chemical Reactions and Equations: Additional ConceptsChemical Reactions and Equations: Additional Concepts Topic 8Topic 8
Reactions that form water or a gas• Some double-replacement reactions in
aqueous solution produce water or a gas (or both) rather than a precipitate.
• In such cases, the water or gas is shown as a product in the net chemical equation, as are the ions that produced it.
• The following example problem illustrates this concept.
Chemical Reactions and Equations: Additional ConceptsChemical Reactions and Equations: Additional Concepts Chemical Reactions and Equations: Additional ConceptsChemical Reactions and Equations: Additional Concepts Topic 8Topic 8
Reactions that form water or a gas
• When hydrochloric acid and potassium hydroxide solutions are mixed, water results, together with an aqueous solution of potassium chloride.
• Write the balanced chemical equation, for this reaction.
Chemical Reactions and Equations: Additional ConceptsChemical Reactions and Equations: Additional Concepts Chemical Reactions and Equations: Additional ConceptsChemical Reactions and Equations: Additional Concepts Topic 8Topic 8
Reactions that form water or a gas
• The balanced chemical equation is the same as the skeleton equation.
Chemical Reactions and Equations: Additional ConceptsChemical Reactions and Equations: Additional Concepts Chemical Reactions and Equations: Additional ConceptsChemical Reactions and Equations: Additional Concepts Topic 8Topic 8
Major Classes of Reactions
• A combustion reaction is one in which a substance rapidly combines with oxygen to form one or more oxides.
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Combustion
• When 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 ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Combustion
Chemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsChemical Reactions and Equations: Basic ConceptsTopic 8Topic 8
Basic Assessment QuestionsBasic Assessment Questions
Question 3
Identify each of the following skeleton equations as representing a synthesis reaction, a combustion reaction, both synthesis and combustion, or decomposition reaction. Balance each equation if necessary.
Topic 8Topic 8
Basic Assessment QuestionsBasic Assessment Questions
synthesis;
Answer 3a
Question 3a Topic 8Topic 8
Basic Assessment QuestionsBasic Assessment Questions
decomposition; already balanced
Answer 3b
Question 3b Topic 8Topic 8