Chemical Equations and Reactions Chapter 8

Key Terms Chemical reaction Chemical equation Coefficient Combustion reaction Synthesis reaction Decomposition reaction Activity series Double-displacement reaction

Describing Chemical Reactions What is a chemical reaction? Reactants -vs- products Evidence of a chemical change… – Change in energy – ppt (precipitate) formed – gas produced new substance – color change formed ex. page 261 table 1

Reactions and Energy Changes Energy can be produced in a reaction (exothermic) Methane + oxygen carbon dioxide + water + energy Energy can be required or absorbed to start a reaction (endothermic) Dinitrogen tetroxide + energy nitrogen dioxide Reactants must contact each other in order for them to react.

Reactions continued Chemical equations are like recipes. They show you how much of each substance is required to form a balanced equation ?CH 4 + ?O 2 ?CO 2 + ?H 2 O Equations can also show the physical states of the reactants and products. Pg 265 table 2

Diatomic Elements BrINClHOF Bromine, Iodine, Nitrogen, Chlorine, Hydrogen, Oxygen and Fluorine all occur in pairs as lone elements Br 2, I 2, N 2, Cl 2, H 2, O 2, F 2

Balancing Chemical Equations Mass of our reactants must equal the mass of the products The number of “X” atoms on one side must equal the number of “X” atoms on the other. ?Na + ?H 2 O ?NaOH + ?H 2 Coefficents must be added..(subscripts cannot be changed) coefficients go where the question marks are Pg Lets try it out!!

Classifying Chemical Reactions There are five types of reactions – Combustion – Synthesis (combination) – Decomposition – Single Displacement (Single Replacement) – Double Replacement (Double Displacement)

Synthesis reaction A + B AB A single compound forms from 2 or more reactants C + O 2 CO 2 Ionic charges can be used to determine the product formed Li +S yields? Two compounds can form a ternary compound (3 elements) CaO(s) + H 2 O(l) Ca(OH) 2 (s)

Decomposition reaction AB A + B Opposite of synthesis (a single compound breaks down into 2 or more elements) 2H 2 O(l) 2H 2 (g) + O 2 (g) Lets practice what we’ve learned so far. Pg 279

Types of Decomposition Elemental decomposition – Start with a compound and it splits into its elements Carbonate decomposition – Metal carbonate → Metal oxide + carbon dioxide Chlorate decomposition – Metal chlorate → Metal chloride + oxygen Hydroxide decomposition – Metal hydroxide → Metal oxide + water

Single Displacement reactions A single element replaces an element from another compound 2Al + 3CuCl 2 2AlCl 3 + 3Cu Activity series Table 4 pg 281 (The lone element must be higher on the chart than the element it is replacing) An element will most likely replace an element below it but not above it The higher they are the more active they are

Single Displacement Continued Metal Displacement – A + BC B + AC – The lone metal will replace the metal in the compound if it is higher on the activity series chart for metals Halogen Displacement – D 2 + EF F 2 + ED – The lone halogen will replace the halogen in the compound if it is higher on the activity series chart for the halogens Let’s try it! Pg 282

Double-Displacement reaction AB + CD AD + CB Similar to single replacement Instead of a single element switching now there are two compounds switching “partners” HCl +NaOH HOH + NaCl

Solubility Chart Use the chart to see if substances are soluble in water or insoluble in water (aq) is used for soluble aqueous (aq) means dissolved in water (s) is used for insoluble solid (s) is for the precipitate (ppt)

Combustion Reactions Combustion reactions Reaction of a carbon based compound (hydrocarbons) and oxygen. C 3 H 8 + 5O 2 3CO 2 + 4H 2 O Only thing that changes is the hydrocarbon: always add oxygen and get carbon dioxide plus water