Chapter 6 Chemical Reactions and Quantities

Chapter 6 Chemical Reactions and Quantities 6.1Chemical Reactions

Chemical Change In a chemical change, • reacting substances form new substances with different compositions and properties • a chemical reaction takes place

Evidence of Chemical Change

Chemical Reactions In a chemical reaction, • a chemical change produces one or more new substances • there is a change in the composition of one or more substances

Chemical Reactions (continued) In a chemical reaction, • old bonds are broken and new bonds formed • atoms in the reactants are rearranged to form one or more different substances

Learning Check Identify the visible evidence of a chemical reaction in each of the following: 1) Methane gas in an outdoor heater burns with a blue flame. 2) Bleach removes stains from a shirt. 3) Bubbles of CO2 are released when baking soda is mixed with vinegar.

Solution 1) Methane gas in an outdoor heater burns with a blue flame. Heat and a flame 2) Bleach removes stains from a shirt. Color change (color removed) 3) Bubbles of CO2 are released when baking soda is mixed with vinegar. Formation of gas (bubbles)

Chemical Equations A chemical equation • gives the chemical formulas of the reactants on the left of the arrow and the products on the right

Symbols Used in Equations Symbols used in chemical equations show • the states of the reactants • the states of the products • the reaction conditions

Chemical Equations are Balanced In a balanced chemical reaction, • atoms are not lost or gained • the number of atoms in the reactants is equal to the number of atoms in the products

A Balanced Chemical Equation In a balanced chemical equation, • there must be the same number of each type of atom on the reactant side and on the product side • numbers called coefficientsare used in front of one or more formulas. Al + S Al2S3 Not balanced 2Al + 3S Al2S3Balanced 2Al = 2Al 3S = 3S

Learning Check State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations: A. P4(s) + 6Br2(l) 4PBr3(g) B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)

Solution A. P4(s) + 6Br2(l) 4PBr3(g) 4 P 4 P 12 Br 12 Br B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s) 2 Al 2 Al 2 Fe 2 Fe 3 O 3 O

Learning Check Determine if each equation is balanced or not. A. Na(s) + N2(g) Na3N(s) B. C2H4(g) + H2O(l) C2H5OH(l)

Solution A. Na(s) + N2(g) Na3N(s) Not balanced 2N 1N 1Na 3Na B. C2H4(g) + H2O(l) C2H5OH(l) Balanced 2C 2C 6H 6H 1O 1O

Equation for A Chemical Reaction

Checking a Balanced Equation

Guide to Balancing Equations

Balancing Chemical Equations STEP 1 Write the equation with the correct formulas. N2(g) + H2(g) NH3(g) STEP 2 Determine if the equation is balanced. No, not all of the atoms are balanced. 2N 1N 2H 3H STEP 3 Balance with coefficients in front of formulas. Balance N N2(g) + H2(g) 2NH3(g)

Balancing Chemical Equations (continued) STEP 3 (continued) Balance H N2(g) + 3H2(g) 2NH3(g) STEP 4 Check that atoms of each element are equal in reactants and products. 2N = 2N 6H = 6H

Learning Check Check the balance of atoms in the following: Fe3O4(s) + 4H2(g) 3Fe(s) +4H2O(l) A. number of H atoms in products 1) 2 2) 4 3) 8 B. number of O atoms in reactants 1) 2 2) 4 3) 8 C. number of Fe atoms in reactants 1) 1 2) 3 3) 4

Solution Fe3O4(s) + 4H2(g) 3Fe(s) +4H2O(l) A. number of H atoms in products 3) 8 (4H2O) B. number of O atoms in reactants 2) 4 (Fe3O4) C. number of Fe atoms in reactants 2) 3 (Fe3O4)

Learning Check Balance each equation and list the coefficients in the balanced equation going from reactants to products. A. __Mg(s) + __N2(g) __Mg3N2(s) 1) 1, 3, 2 2) 3, 1, 2 3) 3, 1, 1 B. __Al(s) + __Cl2(g) __AlCl3(s) 1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, 2

Solution Balance each equation and list the coefficients in the balanced equation going from reactants to products. A. 3) 3, 1, 1 3Mg(s) + 1N2(g) 1Mg3N2(s) B. 3) 2, 3, 2 2Al(s) + 3Cl2(g) 2AlCl3(s)

Equations with Polyatomic Ions

Balancing with Polyatomic Ions STEP 1 Write the equation with the correct formulas. Na3PO4(aq) + MgCl2(aq) NaCl(aq) + Mg3(PO4)2(s) STEP 2 Determine if the equation is balanced. No, not all atoms are balanced. 3Na+ 1Na+ 1PO43 2PO43  1Mg2+ 3Mg2+ 2Cl 1Cl STEP 3 Balance with coefficients in front of formulas. Balance PO43as a unit. 2Na3PO4(aq) Mg3(PO4)2(s)

Balancing with Polyatomic Ions (continued) STEP 3 (continued) Balance Mg 3MgCl2(aq) Mg3(PO4)2(s) Balance Na and Cl 3MgCl2(aq) + 2Na3PO4(aq) 6NaCl(aq) + Mg3(PO4)2(s) STEP 4 Check that atoms of each element are equal in reactants and products. 2PO43–= 2PO43– 3Mg2+ = 3Mg2+ 6Na+ = 6Na+ 6Cl= 6Cl

Learning Check Balance and list the coefficients from reactants to products: A. __Fe2O3(s) + __C(s) __Fe(s) + __CO2(g) 1) 2, 3, 2,3 2) 2, 3, 4, 3 3) 1, 1, 2, 3 B. __Al(s) + __FeO(s) __Fe(s) + __Al2O3(s) 1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1 C. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g) 1) 3, 2, 1, 22) 2, 3, 1, 3 3) 2, 3, 2, 3

Solution A. 2) 2, 3, 4, 3 2Fe2O3(s)+ 3C(s) 4Fe(s) + 3CO2(g) B. 1) 2, 3, 3, 1 2Al(s) + 3FeO(s) 3Fe(s) + 1Al2O3(s) C. 2) 2, 3, 1, 3 2Al(s) + 3H2SO4(aq) 1Al2(SO4)3(aq) + 3H2(g)

Chapter 6 Chemical Reactions and Quantities