Chemical Equation

Chemical Equation• Includes the substances being reacted (reactants), the

substances being formed (products), the phases of each of the substances, the number of moles of each substance, and the resultant energy change.

Reactants Products• Coefficients are placed in front of the substance

symbols to denote a mole ratio that is in accordance with the Law of Conservation of Mass.

HCl (aq) + Zn (s) H2 (g) + ZnCl2 (aq)

(reactants) (products)• This says that hydrochloric acid reacts with zinc metal

to form hydrogen gas and zinc chloride.

Word Equations

• A WORD EQUATION describes chemical change using the names of the reactants and products.

Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water.

methane + oxygen

Reactant ProductCH4 O2 CO2 H2O

+ + 22

carbon dioxide + water

Checking for understandingWrite the word equation:Zn + HCl ZnCl2 + H2

Ca(OH)2 + H3PO4 Ca3(PO4)2 + H2O

6HCl + Fe2O3 2FeCl3 + 3H2O

Balancing Equation

The Law of Conservation of MassMass cannot be created or destroyed by physical or

chemical change. • The elements found in the reactants can be the only

elements found in the products, and there must be equal numbers of moles of those elements on both sides.

HCl (aq) + Zn (s) H2 (g) + ZnCl2 (aq)• Balancing equations involves placing coefficients that act

as multipliers in front of a substance's formula.2 HCl (aq) + Zn (s) H2 (g) + ZnCl2 (aq)

• This shows that 2 moles of HCl are required to react with 1 mole of Zn.

?

Visualizing a Chemical ReactionNa + Cl2 NaCl

___ mole Cl2 ___ mole NaCl___ mole Na

2

10 5 10

2

10 5 10

Visualizing a Chemical ReactionNa + Cl2 NaCl 2 2

Tips for Balancing Equation

2 Cl vs Cl2

Cl2 means that there is one molecule of

diatomic chlorine.

2 Cl means that there are TWO

ATOMS of chlorine.

Diatomic molecules (Br2, I2, N2, Cl2, H2, O2, F2) exist whenever these elements are not in a compound with

another element.

Tips for Balancing Equation

• NEVER CHANGE THE CHEMICAL FORMULA!!! • You can ONLY write coefficients to balance!

3PO4

COEFFICIENT CHEMICAL FORMULA

Separation of NaCl

• In NaCl, there is one Cl-1 ion (since Na is charged +1), but if that chlorine is separated from that compound:

NaCl Na + Cl• Then the Cl’s thus formed will pair up

diatomically, which throws off the balancing:

NaCl Na + Cl2

Ex.1: carbon reacts with oxygen gas to produce carbon dioxide:

already balanced- 1: 1: 1Ex.2: hydrogen gas reacts with oxygen gas to produce water:

balanced ratio- 2: 1: 2

C + O2 CO2

C

O

1 1

2 2

H2 + O2 H2O

H

O

2 2

2 1

2

2x =4

2x =2

2

2x =4

Balance the following equations

• ZnS + O2 ZnO + SO2

2ZnS + 3O2 2ZnO + 2SO2

• Br2 + FeI3 I2 + FeBr3

3Br2 + 2FeI3 3I2 + 2FeBr3<Even and Odd rule>

Start off by putting an even number on the elements that are odd.

1. ___NaClO3 ___NaCl + ___O2

2. ___Fe3O4 + ___H2 ___Fe + ___H2O

Sample Problems:1. Hydrogen + oxygen water

3. Zinc + hydrochloric acid zinc chloride + hydrogen

3. Copper + silver nitrate cupric nitrate + silver

4. Ferric hydroxide iron (III) oxide + water

2 2 3

4 3 4

(Fe Single element)

H2 + O2 H2O22

Zn + HCl ZnCl2 + H22

Cu + AgNO3 Cu(NO3)2 + Ag2(Keep NO3 together)

2

Fe(OH)3 Fe2O3 + H2O2 3(O in multiple comp)

5. Ethane (C2H6) + oxygen carbon dioxide + water

6. Calcium + water calcium hydroxide + hydrogen

7. Potassium + sulfuric acid potassium sulfate + hydrogen

8. Calcium nitrate + aluminum sulfite calcium sulfite + aluminum nitrate

9. Phosphoric acid is formed when crystalline diphosphorus pentoxide is dissolved in water.

2Ca + H2O Ca(OH)2 + H2

K + H2SO4 K2SO4 + H22

C2H6 + O2 + H2OCO2 62 7 4

Ca(NO3)2 + Al2(SO3)3 CaSO3 + Al(NO3)33 3 2

P2O5 + H2O H3PO43 2

Reaction Types

Combustion occur when a compound or element react with oxygen to

release energy and produce an oxideC3H8 + 5O2 3CO2 + 4H2O

+ +

General Form: CXHY + O2 CO2 + H2O

C C CHH

HH

H

H

HH

O OO OO OO OO O

CO O

CO O

CO O

OH H

OH H

OH H

OH H

+ ENERGY

Synthesis ReactionDirect combination reaction

Two elements combine to form a compound

General form: A + B AB

Na

ClNa

Cl

2 Na + Cl2 2 NaCl

ClNa

Na Cl

Formation of a solid: AgCl

AgNO3(aq) + KCl(aq) KNO3 (aq) + AgCl(s)

H

HH

H

Decomposition Reaction

H

HH

HO

Reverse of synthesisa compound decomposes into its original elements

2 H2O 2 H2 O2+

+

OO

O

General form: AB A + B

Be careful!

• DO NOT split the formula and rewrite.• MUST check the diatomic molecule!!!

2 H2O

H2 + O2

H2 + ODIATOMIC MOLECULE!!!!!!!!!!!WRONG!

CORRECT!

Single Replacement Reactionreplace one element from a compound with

another element

CuCl2 + Zn ZnCl2 Cu+

General form: A + BC B + AC where A is a metal, or

A + BC C + BA where A is a non-metal

ZnClCl Cu + ClCl

Zn Cu+

Be careful!

• DO NOT split the formula and rewrite.• MUST check the ion and charges!!!

Zn + HNO3

Zn(NO3)2 + H2

ZnNO3 + H

Charges are not balanced!WRONG!

CORRECT!

- 1+2 Diatomic Molecule

Single Replacement Reaction Practice

Al + Ag2CO3

1. Label the charges above each ion

2. Check the activity series 3. Write the product by

balancing the charges4. Balance the reaction

Al + Ag2CO3 Al2(CO3)3 + Ag2 3

+1 -2+3

ABOVE CAN REPLACE BELOW

Mg + AlCl3

Al + MgCl2

Predict if these reactions will occur

Al + MgCl2

Can magnesium replace aluminum?

Activity Series

YES, magnesium is more reactive than aluminum.

2 23 3

Can aluminum replace magnesium?

Activity Series

NO, aluminum is less reactive than magnesium.

Therefore, no reaction will occur.

No reaction

MgCl2 + Al No reaction

The question we must ask is can the single element replace its counterpart? metal replaces metal or nonmetal replaces nonmetal.

Order of reactants DOES NOT

determine how they react.

Double Displacement ReactionTwo solutions react to form a precipitate (solid) and another solution.

MgO + CaS MgS + CaO

General Form: AB + CD AD + CB

SOMg Ca

+O S

Mg Ca+

Be careful!

• DO NOT split the formula and rewrite.• MUST check the ion and charges!!!

K2CrO4 + 2AgNO3

KNO3 + Ag2CrO4

KNO3 + AgCrO4

Charges are not balanced!WRONG!

CORRECT!

+ 1 - 2

Precipitate• Insoluble ions remain together. • This is because the attractions

between the ions are too strong for water molecules to tear apart.

• The ions come together and form crystals, which make the solution cloudy.

• The crystals are pulled to the bottom of the solution by gravity, forming a PRECIPITATE.

K2CrO4 + 2AgNO3 Ag2CrO4 + 2KNO3

Solubility Rules

• Solubility rules can used to determine if a reaction will occur in a double displacement reaction.

• If both the products are soluble (form ions in solution), then no reaction has occurred.

Double Displacement Reaction3CoCl2(aq) + 2Na3PO4(aq) Co3(PO4)2(s) + 6NaCl(aq)

Will this reaction occur?

A reaction will occur only if the following

will be produced1)Gas

2)Solid precipitate

Solubility table

Precipitate

Verifying SolubilityUse your solubility chart to verity if the compound is soluble in water?

a) MgCO3

b) AgNO3

c) MgCl2

d) Na3PO4

e) KOH

InsolubleSolubleSolubleSolubleInsoluble

Double Replacement Reaction Practice

Na3PO4 (aq) + Mg(NO3)2 (aq)

1. Label the charges above each ion2. Write the product by balancing

the charges3. Check solubility using the rules4. Label the correct state5. Balance the reaction

+1 -3 +2 -1

Na3PO4 (aq) + Mg(NO3)2 (aq) NaNO3 + Mg3(PO4)2

INSOLUBLE

NaNO3 (aq) + Mg3(PO4)2(s)2 3 6

Checking for understandingComplete the chartType of reaction

General Form Example

1.

2.

3.

4.

5.

Oxidation vs. Reductiondriven by the loss of electrons (oxidation) and the

gain of electrons (reduction).

Oxidation-Reduction Reaction

• Oxidation is loss of electrons.

• Reduction is gain of electrons.

• There is a very easy way to do this. As long as you remember that you are talking about electron transfer:

Neutralizationoccur when an acid (most compounds starting with H) and a base

(most compounds ending in OH) react to form a salt and water.Acid + Base Salt + Water

+ +

General Form: HX + MOH MX + H2O

where X and M are elements

H Cl-Na+

O HH

OHCl-Na+

Checking for understandingExplain in exactly 10 words each process. Your sentences do have to make sense:OxidationReductionNeutralization

Stoichiometry

Stoichiometry Road Map

aA + bB cC + dD

Mass A

AtomsMolecules

A

Mol A Mol B

Mass B

AtomsMolecules

B

Mol Ratio

Molar mass

6.022 x 1023

Molar

mass

6.022 x 10 23

3 A + 4 B 2 D + 1 F

How many moles of F are produced from 1.00 mol of A?

1 mol A

3 mol A

1 mol F= 0.333 mol F

How many moles of D are produced from 5.00 mol of B?

5 mol B

4 mol B

2 mol D

= 2.50 mol D

How many moles of lithium carbonate are produced when 5.3 mol CO2 are reacted?

CO2(g) + 2LiOH(s) Li2CO3(s) + H2O(l)

1. What is your starting point?2. What is your ending point?

5.3 mol of CO2

mol of Li2CO3

5.3 mol CO2

1 mol CO2

1 mol Li2CO3

= 5.3 mol Li2CO3

3 A + 4 B 2 D + 1 FHow many grams of F are produced from 1.00 mol of A? If MM of F is 10.0g/mol.

1 mol A

3 mol A

1 mol F= 3.33g F

How many grams of D are produced from 5.00 mol of B? MM of D is 20.0g/mol

5 mol B

4 mol B

2 mol D

= 50.0g D

1 mol F

10 g F

1 mol D

20 g D

What is the mass of glucose (C6H12O6) produced from 3.00 mol of water (H2O)?

6CO2(g) + 6H2O(l) C6H12O6(s) + 6O2(g)

3 mol H2O

1. What is your starting point?2. What is your ending point?

3.00 mol of H2Og of C6H12O6

6 mol H2O

1 mol C6H12O6

1 mol C6H12O6

=90.1 g C6H12O6

180.81g C6H12O6

6CO2(g) + 6H2O(l) C6H12O6(s) + 6O2(g)

What is the mass of oxygen (O2) produced from 2.50 mol of water (H2O)?

1. What is your starting point?2. What is your ending point?

2.50 mol of H2Og of O2

2.5 mol H2O

6 mol H2O

6 mol O2

1 mol O2

32.0 g O2

=80.0 g O2

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)

How many moles of NO are formed from 824 g of NH3?

1. What is your starting point?2. What is your ending point?

824 g of NH3

mol of NO

824 g NH3

17.03g

1 mol NH3

4 mol NH3

4 mol NO

= 48.4 mol NO

3 A + 4 B 2 D + 1 FHow many grams of F are produced from 5.00g of A? If MM of F is 10.0g/mol and MM of A is 25.0g/mol

1 mole A

3 mole A

1 mole F= 0.677g F

How many grams of D are produced from 5.00g of B? MM of D is 20.0g/mol and MM of B is 10.0g/mol

1 mole B

4 mole B

2 mole D

=5.00g D

1 mole F

10 g F

1 mole D

20 g D

5 g A

25 g A

5 g B

10 g B

Sn(s) + 2HF(g) SnF2(s) + H2(g)

How many grams of SnF2 are produced from the reaction of 30.00 g HF?

1. What is your starting point?2. What is your ending point?

30.00 g of HFg SnF2

1 mol HF

2 mol HF

1 mol SnF2

= 117.5g SnF2

1 mol SnF2

156.71 g SnF2 30.00g HF

20.01g HF

Working a Stoichiometry Problem6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed?

1. Identify reactants and products and write the balanced equation.

Al + O2 Al2O3

b. What are the reactants?a. Every reaction needs a yield sign!

c. What are the products?

d. What are the balanced coefficients?

4 3 2

=6.50 g Al

? g Al2O3

1 mol Al

26.98 g Al 4 mol Al

2 mol Al2O3

1 mol Al2O3

101.96 g Al2O3

6.50 x 2 x 101.96 ÷ 26.98 ÷ 4

= 12.3 g Al2O3

1. What is your starting point? 6.50 g of Aluminum2. What is your ending point? g of aluminum oxide

Al + O2 Al2O34 3 2