Presentation on theme: "Chemical Reactions Chapter 11. Describing Chemical Reactions Essential Question: How does one write a proper word, skeleton or chemical equation?"— Presentation transcript:
Chemical Reactions Chapter 11
Describing Chemical Reactions Essential Question: How does one write a proper word, skeleton or chemical equation?
Writing Chemical Equations How do you describe what has happened in a chemical reaction? Recall from Chapter 2 the shorthand method of describing a chemical reaction: ReactantsProducts
Word Equations iron + oxygenIron(III) oxide hydrogen peroxidewater + oxygen methane + oxygencarbon dioxide + water What does the arrow in these word equations indicate?
Skeleton Equations Fe + O 2 Fe 2 O 3 H 2 O 2 H 2 + O 2 CH 4 + O 2 CO 2 + H 2 O A skeleton equation is an equation that does not indicate the relative amounts of the substance involved.
Balancing Chemical Equations How would you write a word equation for the production of a tricycle? frame + wheel + handlebar + pedal tricycle This doesn’t tell about the relative amounts involved
Skeleton Equations How would you write a skeleton equation for the production of a tricycle? F + W + H + P FW 3 H 2 P 2 Notice: This still doesn’t tell about the relative amounts involved
Balanced Equations How would you write a balance chemical equation for the production of a tricycle? F + 3W + 2H + 2PFW 3 H 2 P 2 Notice: You must use coefficients to indicate the relative amounts involved.
Balancing Chemical Reactions
Combustion of Methane
Production of Hydrogen Chloride
Rules for Writing Balanced Chemical Equations See the table at the top of page 327. Balancing Chemical Equations – Computer lab activity
Balance These Equations AgNO 3 + H 2 S Ag 2 S + HNO 3 Zn(OH) 2 + H 3 PO 4 Zn 3 (PO 4 ) 2 + H 2 0 FeCl 3 + Ca(OH) 2 Fe(OH) 3 + CaCl 2 Ag 2 S(s) + Al(s)Ag(s) + Al 2 S 3 (g)
Types of Chemical Reactions Essential Question: What are the five general types of chemical reactions, and how can you predict the products of these reactions?
Classifying Reactions Reactions fall into five general categories: Combination Reactions Decomposition Reactions Single Replacement Reactions Double Replacement Reactions Combustion Reactions
Combination Reactions Two or more substances forming a single new substance. Our analogy: like a marriage What distinguishes combination reactions is the presence of only one product.
Also known as Synthesis reactions. Examples: 2Mg(s) + O 2 (g)2MgO 2K(s) + Cl 2 (g)2KCl(s) Fe(s) + S(s)FeS(s) 2Fe (s) + 3S(s) Fe 2 S 3 (s)
Decomposition Reactions A single compound breaks down into two or more simpler products. Our analogy: a divorce What distinguishes a decomposition reaction is a single reactant.
Examples: 2HgO(s) 2Hg(l) + O 2 (g) 2H 2 O (l) 2H 2 (g) + O 2 (g) 2HIH 2 (g) + I 2 (s) electricity
Single-Replacement Reactions One element replaces another element in a compound. Our analogy: Date-stealing What distinguishes a S-R reaction is an uncombined element in the reactants with a different uncombined element in the products.
Will S-R Reactions Occur? Whether one metal will replace another in a compound depends their respective reactivities. A reactive metal will replace any metal below it in the reactivity series. See Table 11.2 on page 333. What about the reactivity of the halogens?
Activity Series of the Metals
The Activity Series of the Metals
Double-Replacement Reactions A chemical change involving an exchange of positive ions between two compounds. Our analogy: Date-Swapping
Double-Replacement Reactions Examples: Na 2 S(aq) + Cd(NO 3 ) 2 (aq) CdS(s) + 2NaNO 3 (aq) 2NaCN(aq) + H 2 SO 4 (aq) 2HCN(g) + Na 2 SO 4 (aq) Ca(OH) 2 (aq) + 2HCl(aq) CaCl 2 (aq) + 2H 2 O(l)
Double-Replacement Reactions For a D-R reaction to occur, one of the following is usually true: –One of the products is a solid that precipitates out –One of the products is a gas –One of the products is a molecular compound, such as water
Combustion Reactions An element or a compound reacts with oxygen, often producing light and heat. Complete combustion = a hydrocarbon reacting with oxygen to produce ONLY carbon dioxide and water as the products.
Combustion Examples: 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O(l) 2C 6 H 6 (l) + 15O 2 12CO 2 (g) + 6H 2 O(g) 2Mg(s) + O 2 (g)2MgO(s) Which of these are complete combustion?
Reactions in Aqueous Solution Essential Question: What does a net ionic equation show, and how can one predict the formation of a precipitate in a double-replacement reaction?
Net Ionic Equations A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge. All ions that are unchanged from the reactants side to the products side of the equation are eliminated.
Net Ionic Equations Begin with a double-replacement reaction: AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq) Write the complete ionic equation: Ag + (aq) + NO 3 – (aq) + Na + (aq) + Cl – (aq) AgCl(s) + Na + (aq) + NO 3 – (aq)
Net Ionic Equations, cont. Eliminate the ions that are “spectators” Ag + (aq) + NO 3 – (aq) + Na + (aq) + Cl – (aq) AgCl(s) + Na + (aq) + NO 3 – (aq) Ag + (aq) + NO 3 – (aq) + Na + (aq) + Cl – (aq) AgCl(s) + Na + (aq) + NO 3 – (aq) What remains is the Net Ionic Equation Ag + (aq) + Cl – (aq)AgCl(s)
Formation of Precipitates One can predict the formation of a precipitate by using the general rules for solubility for ionic compounds. See Table 11.3 on page 344, or see the Reference Tables.
Solubility Rules for Ionic Compounds
Predicting the Formation of a Precipitate
Formation of Precipitates Will a precipitate form when the following aqueous solutions are mixed? AgNO 3 and Na 2 SO 4 NH 4 Cl and Ba(NO 3 ) 2 CaCl 2 and K 2 SO 4 Hg(NO 3 ) 2 and HCl Yes, No, Yes, No