Chapter 7: Chemical Reactions Chemical reaction: conversion of substances into different substances (by rearranging atoms) Reactants: substances present before reaction Products: substances present after reaction Balancing chemical equations Law of conservation of mass: H 2 + O 2 H 2 O Chemical equation: represents a reaction on paper Reactants Products Phase labels: show the phase of reactants or products (s) : Tips for balancing: 1. Leave elemental substances for last: CH 4 + O 2 CO 2 + H 2 O (l) : (g) : (aq) : In an even/odd issue, try doubling all other coefficients C 4 H 10 + O 2 CO 2 + H 2 O Always make sure all coefficients are reduced to the simplest whole numbers! ch7 Page 1 ch7 Page 2
Balancing If an element appears in one compound on each side, balance that element first, making the least common multiple on both sides (2b on prelab) H 3 PO 3 H 3 PO 4 + PH 3 Double displacement, solubility, and precipitation Double displacement reaction: two ionic reactants swap their ions AgNO 3 (aq) + NaI(aq) If polyatomic ions are identical on both sides, group them when counting Na 2 SO 4 + Ca(NO 3 ) 2 NaNO 3 + CaSO 4 Use the chemical equations worksheet to practice writing and balancing chemical equations. Write the balanced chemical equation with phase labels for the following word description: Solid sodium and liquid water combine to create sodium hydoxide solution and hydrogen gas. 1. 5. Write ion pairs for reactants Swap ions, make new +/-pairs, writing + ion first Make formulas for possible products from new ion pairs Balance if necessary Predict phase labels of products ch7 Page 3 ch7 Page 4
Solubility of ionic compounds Precipitation reaction Some ionic compounds easily dissolve in water (soluble) Some never dissolve in water (insoluble) Precipitate: insoluble (s) product of a chemical reaction AgNO 3 (aq) + NaI(aq) Solubility Rules for Ionic Compounds The following table will be given on the exam exactly as shown here. Compounds Containing the Following Ions Are Mostly Soluble Li +, Na +, K +, NH 4 + nitrate, acetate chloride, bromide, iodide sulfate Exceptions None None When any of these ions pairs with Ag +, Hg 2 2+, or Pb 2+, the compound is insoluble When sulfate pairs with Sr 2+, Ba 2+, Pb 2+, or Ca 2+ the compound is insoluble Write the balanced chemical equation for the reaction of lead(ii) nitrate and sodium iodide solutions. If a precipitate forms, what is its name? Compounds Containing the Following Ions Are Mostly Insoluble hydroxide, sulfide carbonate, phosphate Exceptions When either of these ions pairs with Li +, Na +, K +, or NH 4+, the compound is soluble When sulfide pairs with Ca 2+, Sr 2+, or Ba 2+, the compound is soluble When hydroxide pairs with Ca 2+, Sr 2+, or Ba 2+, the compound is slightly soluble (for many purposes, these may be considered insoluble) When either of these ions pairs with Li +, Na +, K +, or NH 4+, the compound is soluble Write the balanced chemical equation for the reaction of potassium sulfate and sodium phosphate solutions. Na 3 PO 4 Ca 3 (PO 4 ) 2 CaI 2 PbI 2 Fe(OH) 3 Ca(OH) 2 K 2 CO 3 CuCO 3 ch7 Page 5 ch7 Page 6
Other reaction types 1. Combustion reaction(fire or flame are produced) carbon-containing compound + O 2 CO 2 + H 2 O Write a balanced chemical equation for the complete combustion of propane, C 3 H 8. Other reaction types Single-displacement reaction: 1 element is replaced by another (an element + a compound another element + another compound) 2 Al(s) + Fe 2 O 3 (s) 2 Fe(l) + Al 2 O 3 (s) 2 Na(s) + 2H 2 O(l) 2 NaOH(aq) + H 2 (g) Decomposition reaction: 1 reactant decomposes into 2 or more products H 2 O 2 (aq) catalystsspeed up reactions but are not consumed by the reaction -they are common in decomposition reactions H 2 O 2 (aq) Synthesis reaction: 2 or more reactants form 1 product Write the synthesis reaction that silver and oxygen will undergo. ch7 Page 7 ch7 Page 8
Review: reaction types Double displacement Combustion Decomposition Single displacement Synthesis ch7 Page 9