3.7 chem. eqs 3.8 balancing chem. eqs - department of...

3.7 Chem. Eqs&

3.8 Balancing Chem. Eqs

Copyright © Houghton Mifflin Company. All rights reserved. 3–2

Chemical Equations

A chemical equation gives the chemical formulas of the reactants on the left of the arrow and the products on the right.

Reactants Product

C(s)

O2 (g)CO2 (g)


Symbols Used in Equations

Symbols used in chemicalequations show

• the states of the reactants.

• the states of the products.

• the reaction conditions.

TABLE


Chemical Equations are Balanced

In a balancedchemical reaction• atoms are not

gained or lost.

• the number of reactant atoms is equal to the number of product atoms.


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 of a balanced equation.

• numbers called coefficients are used in front of one or more formulas.

Al + S Al2S3 Not Balanced2Al + 3S Al2S3 Balanced

2 Al = 2 Al3 S = 3 S


Learning Check

State the number of atoms of each element on thereactant side and the product side for each of thefollowing balanced equations.

A. P4(s) + 6Br2(l) 4 PBr3(g)

B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)


Solution

A. P4(s) + 6Br2(l) 4 PBr3(g)4 P 4 P12 Br 12 Br

B. 2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)2 Al 2 Al2 Fe 2 Fe3 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

Determine if each equation is balanced or not.

A. Na(s) + N2(g) Na3N(s)No. 2 N on reactant side, 1 N on product side.

1 Na on reactant side, 3 Na on product side.

B. C2H4(g) + H2O(l) C2H5OH(l)Yes. 2 C = 2 C

6 H = 6 H1 O = 1 O


Guide to Balancing a Chemical Equation

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings


To balance the following equation, Fe3O4(s) + H2(g) Fe(s) + H2O(l)

• work on one element at a time.• use only coefficients in front of formulas.• do not change any subscripts.Fe: Fe3O4(s) + H2(g) 3Fe(s) + H2O(l)

O: Fe3O4(s) + H2(g) 3Fe(s) + 4H2O(l)

H: Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)

Steps in Balancing an Equation


1. Write the equation with the correct formulas.NH3(g) + O2(g) NO(g) + H2O(g)

2. Determine if the equation is balanced.No, not all atoms are balanced.

3. Balance with coefficients in front of formulas. 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

4. Check that atoms of each element are equal in reactants and products.

4 N (4 x 1 N) = 4 N (4 x 1 N)12 H (4 x 3 H) = 12 H (6 x 2 H)10 O (5 x 2 O) = 10 O (4 O + 6 O)

Balancing Chemical Equations


Equation for A Chemical Reaction


Checking a Balanced Equation

Reactants Products1 C atom = 1 C atom4 H atoms = 4 H atoms4 O atoms = 4 O atoms


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

Learning Check


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)

Solution


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

Learning Check


A. 3) 3, 1, 13Mg(s) + 1N2(g) 1Mg3N2(s)

B. 3) 2, 3, 2

2Al(s) + 3Cl2(g) 2AlCl3(s)

Solution


Equations with Polyatomic Ions


Balancing with Polyatomic IonsMgCl2(aq) + Na3PO4(aq) NaCl(aq) + Mg3(PO4)2(s)

Balance PO43- as a unit

MgCl2(aq) + 2Na3PO4(aq) NaCl(aq) + Mg3(PO4)2(s)2 PO4

3- = 2 PO43-

Balance Mg and Cl3MgCl2(aq) + 2Na3PO4(aq) 6NaCl(aq) + Mg3(PO4)2(s)

3 Mg2+ = 3 Mg2+

6 Na+ = 6 Na+

6 Cl- = 6 Cl-


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, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3

Learning Check


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)

Solution

3.7 chem. eqs 3.8 balancing chem. eqs - department of...

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