2. Chemical Reactions Chapter 10

3. Section 10.1 – Reactions and Equations 1. Chemical Reactions The process by which one or more substances are rearranged to form different substances is called a chemical reaction.chemical reaction Evidence of a chemical reaction –Change in temperature –Change in color –Odor, gas, or bubbles may form.

4. 2. Representing Chemical Reactions Chemists use statements called equations to represent chemical reactions. Reactants are the starting substances.Reactants Products are the substances formed in the reaction.Products Chemical equations do not express numerical equalities as do mathematical equations because the reactants are used up as the products form during the reaction. Chemists use an arrow rather than an equal sign to show the direction of the reaction and is used to separate the reactants from the products. Reactants are written on the left, products on the right Symbols are used to show the states of the reactants and products This table summarizes the symbols used in chemical equations.

5. Representing Chemical Reactions (cont.) Word equations Word equations are statements used to indicate the reactants and products of chemical reactions aluminum (s) + bromine (g) → aluminum bromide (s) This word equation reads as “ aluminum and bromine react to produce/yield aluminum bromide”.

6. Representin g Chemical Reactions (cont.) Skeleton equations Skeleton equations use symbols and formulas to represent the reactants and products rather than words. Al(s) + Br 2 (g) → AlBr 3 (s) Skeleton equations lack information about how many atoms are involved in the reaction. Chemical equations A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.chemical equation Chemical equations must show that matter is conserved during a reaction

7. 3. Balancing Chemical Equations This figure shows the balanced equation for the reaction between aluminum and bromine. A coefficient in a chemical equation is the number written in front of a reactant or product.coefficient They describe the lowest whole-number ratio of the amounts of all the reactants and products. The most fundamental law in chemistry is the Law of Conservation of Mass. Balanced equations show this law.

8. Balancing Chemical Equations (cont.) Steps for balancing equations 1.Write the skeleton equation for the reaction Make sure that the chemical formulas correctly represent the substances. An arrow separates the reactants from the products, and a plus sign separates multiple reactants and products. Show the physical states of all reactants and products. 2.Count the atoms of the elements in the reactants. If a reaction involves identical polyatomic ions in the reactants and products, count ions as if they are elements.

9. Balancing Chemical Equations (cont.) 3.Count the atoms of the elements in the products. 4.Change the coefficients to make the number of atoms of each element equal on both sides of the equation. Never change a subscript in a chemical formula to balance an equation because doing so changes the identity of the substance.

10. Balancing Chemical Equations (cont.) 5.Write the coefficients in their lowest possible ratio. The coefficients should be the smallest possible whole numbers. 6.Check your work. Make sure that the chemical formulas are written correctly. Check that the number of atoms of each element is equal on both sides of the equation

11. Section 10.2 – Classifying Chemical Reactions 4. Types of Chemical Reactions Chemists classify reactions in order to organize the many types. 1.A synthesis reaction is a reaction in which two or more substances react to produce a single product.synthesis reaction When two elements react, the reaction is always a synthesis reaction. 2.In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.combustion reaction This can also be type of synthesis reaction. Combustion of hydrocarbons always produces water vapor and carbon dioxide.

12. Types of Chemical Reactions (cont.) 3.A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.decomposition reaction Essentially the opposite of synthesis reactions. Often require an energy source, such as heat, light, or electricity, to occur. Table 9.4 summarizes different ways to predict the products of a chemical reaction.

13. Types of Chemical Reactions (cont.) 4.A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.single replacement reaction A + BX → AX + B a.One type of single replacement reaction is one in which a metal replaces a hydrogen in a water molecule. b.Another type occurs when one metal replaces another metal in a compound dissolved in water. A metal will not always replace a metal in a compound dissolved in water because of differing reactivities. A metal’s reactivity is its ability to react with another substance. An activity series can be used to predict if reactions will occur.

14. Types of Chemical Reactions (cont.) c.A third type involves the replacement of a nonmetal in a compound by another nonmetal. Halogens frequently replace other halogens in these replacement reactions. Halogens also have different reactivities and do not always replace each other. 5.Double replacement reactions occur when ions exchange between two compounds.Double replacement reactions Positive and negative ions of two compounds switch places. All double replacement reactions produce either water, a precipitate, or a gas. The solid product produced during a chemical reaction in a solution is called a precipitate.precipitate

15. Section 10.3 – Reactions in Aqueous Solutions 5. Aqueous Solutions An aqueous solution contains one or more dissolved substances (called solutes) in water.aqueous solutionsolutes There are many possible solutes. Sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions. Other solutes are molecular compounds that form ions when they dissolve, called acids. Ionic compounds can also be solutes in aqueous solutions. When ionic compounds dissolve in water, their ions separate in a process called dissociation. The solvent is the most plentiful substance in a solution.solvent Water is always the solvent in an aqueous solution. These reactions are always double-replacement.

16. 6. Reactions That Form Precipitates Some double-replacement reactions that occur in aqueous solutions produce precipitates when the new compound is not soluble in water. For example: Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide. 2 NaOH (aq) + CuCl 2 (aq) → 2 NaCl (aq) + Cu(OH) 2 (s) Using a solubility table will help to predict whether a product will be soluble and therefore whether a precipitate will form.

17. Reactions That Form Precipitates (cont.) Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations. complete ionic equations 2 Na + (aq) + 2 OH – (aq) + Cu 2+ (aq)+ 2 Cl – (aq) → 2 Na + (aq) + 2 Cl – (aq) + Cu(OH) 2 (s) Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations.spectator ions Formulas that include only the particles that participate in reactions are called net ionic equations.net ionic equations Net ionic equations are written from complete ionic equations by crossing out all spectator ions. 2 OH – (aq) + Cu 2+ (aq) → Cu(OH) 2 (s)

18. 7. Reactions That Form Water Some double-replacement reactions that occur in an aqueous solution produce more water molecules. Unlike reactions in which a precipitate forms, no evidence of a chemical reaction is observable because water is colorless, odorless and already makes up most of the solution. For example, HBr (aq) + NaOH (aq) → H 2 O (l) + NaBr (aq) The complete ionic equation for this reactions shows these ions: H + (aq) + Br - (aq) + Na + (aq) + OH - (aq) → H 2 O (l) + Na + (aq) + Br - (aq) Without spectator ions: H + (aq) + OH – (aq) → H 2 O (l). These reactions are a special type of double-replacement reaction, called acid-base reactions.

19. 8. Reactions That Form Gases A third type of double-replacement reaction that occurs in aqueous solutions result in the formation of a gas. Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide. For example, 2 HI (aq) + Li 2 S (aq) → H 2 S (g) + 2 LiI (aq) Another example is mixing hydrochloric acid and baking soda, which produces carbon dioxide gas. HCl (aq) + NaHCO 3 (aq) → H 2 CO 3 (aq) + NaCl (aq) H 2 CO 3 (aq) decomposes immediately. H 2 CO 3 (aq) → H 2 O (l) + CO 2 (g)

20. Reactions That Form Gases (cont.) Reaction 1 HCl (aq) + NaHCO 3 (aq) → H 2 CO 3 (aq) + NaCl (aq) Reaction 2 H 2 CO 3 (aq) → H 2 O (l) + CO 2 (g) Combined equation HCl (aq) + NaHCO 3 (aq) + H 2 CO 3 (aq) → H 2 CO 3 (aq) + NaCl (aq) + H 2 O (l) + CO 2 (g) Overall equation HCl (aq) + NaHCO 3 (aq) → H 2 O (l) + CO 2 (g) + NaCl (aq) The two reactions can be combined and represented by a single chemical reaction.

21. IB Menu Click on an image to enlarge.

22. IB 1

23. IB 2

24. IB 3

25. IB 4

26. IB 5

27. IB 6

28. IB 7

29. IB 8

30. IB 9

31. IB 10

32. IB 11

33. IB 12

34. CIM Table 9.2 Steps for Balancing Equations Figure 9.15 The Forming of a Precipitate Table 9.4 Types of Chemical Reactions

35. Help Click any of the background top tabs to display the respective folder. Within the Chapter Outline, clicking a section tab on the right side of the screen will bring you to the first slide in each respective section. Simple navigation buttons will allow you to progress to the next slide or the previous slide. The “Return” button will allow you to return to the slide that you were viewing when you clicked either the Resources or Help tab. The Chapter Resources Menu will allow you to access chapter specific resources from the Chapter Menu or any Chapter Outline slide. From within any feature, click the Resources tab to return to this slide. To exit the presentation, click the Exit button on the Chapter Menu slide or hit Escape [Esc] on your keyboards while viewing any Chapter Outline slide.

36. End of Custom Shows This slide is intentionally blank.