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Chemical Reactions and Equations: Recognize, Represent, and Balance

Learn about chemical reactions, their evidence, and how to represent them with equations. Understand the importance of balancing equations and classify different types of reactions.

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Chemical Reactions and Equations: Recognize, Represent, and Balance

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  1. Section 9.1 Reactions and Equations • Recognizeevidence of chemical change. chemical change:a process involving one or more substances changing into a new substance • Representchemical reactions with equations. • Balancechemical equations. chemical reaction reactant product chemical equation coefficient Chemical reactions are represented by balanced chemical equations. Section 9-1

  2. Chemical Reactions • The process by which one or more substances are rearranged to form different substances is called a ___________________________ • This involves a chemical change – where you change the identity of the substance. Section 9-1

  3. Chemical Reactions (cont.) • Evidence of a chemical reaction • Change in temperature • Exothermic (higher T) vs Endothermic (lower T) • Change in color • Odor, gas, or bubbles may form. • Form a precipitant (????) • Emission of Light Section 9-1

  4. Chemists use statements called equations to represent chemical reactions. • ______________are the starting substances. • ______________are the substances formed in the reaction. Section 9-1

  5. Representing Chemical Reactions (cont.) • In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) reads as “aluminum and bromine react to produce aluminum bromide”. • Skeleton equations use symbols and formulas to represent the reactants and products. Al(s) + Br(l) → AlBr3(s) • Skeleton equations lack information about how many atoms are involved in the reaction. Section 9-1

  6. Representing Chemical Reactions (cont.) • A _____________________is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction. Section 9-1

  7. Balancing Chemical Equations • This figure shows the balanced equation for the reaction between aluminum and bromine. Section 9-1

  8. Balancing Chemical Equations (cont.) • A ______________________in a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products. • So what are the coefficients on the previous reaction? • *Table 9.2 in book shows steps for balancing equations Section 9-1

  9. Why balance equations? • One of the most fundamental laws in chemistry is the law of conservation of mass. • Balanced equations show this law. • A balanced equation is also like a recipe. Section 9-1

  10. Balancing Chemical Equations (cont.) Section 9-1

  11. Section 9.1 Assessment Which of the following is NOT a chemical reaction? A.a piece of wood burning B.a car rusting C.an ice cube melting into water D.red litmus paper turning blue • A • B • C • D Section 9-1

  12. Section 9.1 Assessment What is the coefficient of bromine in the equation 2Al(s) + 3Br2(l) → 2AlBr3(s)? A.1 B.2 C.3 D.6 • A • B • C • D Section 9-1

  13. Section 9.2 Classifying Chemical Reactions • Classify chemical reactions. metal: an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny • Identify the characteristics of different classes of chemical reactions. Section 9-2

  14. Section 9.2 Classifying Chemical Reactions (cont.) synthesis reaction combustion reaction decomposition reaction single-replacement reaction double-replacement reaction precipitate There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions. Section 9-2

  15. Types of Chemical Reactions • Chemists classify reactions in order to organize the many types. • Why do this? • Help predict products before a reaction happens. (Table 9.4 in book) • A ________________or_________________ is a reaction in which two or more substances react to produce a single product. Section 9-2

  16. Types of Chemical Reactions (cont.) • When two elements react, the reaction is always a synthesis reaction. Section 9-2

  17. Types of Chemical Reactions • A __________________________is one in which a single compound breaks down into two or more elements or new compounds. • Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur. • H2O → H2 + O2 Section 9-2

  18. Types of Chemical Reactions (cont.) • In a ______________________oxygen combines with a hydrocarbon (made mostly of C and H) and releases carbon dioxide, water, heat, and light. • CH4 + O2 → CO2 + H2O Section 9-2

  19. Types of Chemical Reactions • A reaction in which the atoms of one element replace the atoms of another element in a compound is called a _____________________________ A + BX → AX + B “The Player at the Prom” Section 9-2

  20. Replacement Reactions (cont.) • _______________________occur when ions exchange between two compounds. • “The Perfect Prom” Section 9-2

  21. Replacement Reactions (cont.) • The solid product produced during a chemical reaction in a solution is called a ______________________. • All double replacement reactions produce either water, a precipitate, or a gas. Section 9-2

  22. Section 9.2 Assessment Which of the following is NOT one of the four types of reactions? A.deconstructive B.synthesis C.single replacement D.double replacement • A • B • C • D Section 9-2

  23. Section 9.2 Assessment The following equation is what type of reaction? KCN(aq) + HBr(aq) → KBr(aq) + HCN(g) A.deconstructive B.synthesis C.single replacement D.double replacement • A • B • C • D Section 9-2

  24. Section 9.3 Reactions in Aqueous Solutions • Describe aqueous solutions. • Write complete ionic and net ionic equations for chemical reactions in aqueous solutions. • Predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas. solution: a uniform mixture that might contain solids, liquids, or gases Section 9-3

  25. Section 9.3 Reactions in Aqueous Solutions (cont.) aqueous solution solute solvent complete ionic equation spectator ion net ionic equation Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases. Section 9-3

  26. Aqueous Solutions • An ________________________contains one or more dissolved substances (called solutes) in water. • The solvent is the most plentiful substance in a solution. Section 9-3

  27. Aqueous Solutions (cont.) • Water is always the solvent in aqueous solutions. • There are many possible solutes: • ie: sugar, alcohol • Compounds that produce hydrogen ions in aqueous solutions are acids. • Ionic compounds can also be solutes in aqueous solutions. • When ionic compounds dissolve in water, their ions separate in a process called dissociation. • Gatorade and electrolytes !!! Section 9-3

  28. Types of Reactions in Aqueous Solutions • When two solutions that contain ions as solutes are combined, the ions might react. • If they react, it is always a ____________________________ reaction. • Three products can form: • precipitates, • water, or • gases. Section 9-3

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