Unit #12 Chemical Reactions

Part 2

Predicting Products

Review

• A chemical reaction is the rearrangement of atoms to form new substance(s). Reactant(s) appear on the left, and product(s) appear on the right.

reactants product

• Example: 2 H2 + O2 2 H2O

• When we look at any chemical reaction, in order for it to be accurate, it must show that the law of conservation of mass is obeyed.

Law of Conservation of Mass• mass is neither created nor destroyed in a

chemical reaction• total mass stays the same• atoms can only rearrange• So, we need to make sure that there are the

same number of each type of atom on each side of the chemical equation.

• To do this, we add coefficients in front of the compounds until these atoms are “balanced.”

• Refresh your memory by balancing these equations:

__MgCl2 +__NaOH __Mg(OH)2 +__NaCl

__Fe2(SO4)3 +__KOH __K2SO4 +__Fe(OH)3

22

6 3 2

2 H2 + O2 → 2 H2O3 Mg + N2 → Mg3N2

Synthesis Reaction

A reaction in which two or more elements form a compound.

Synthesis• 2 or more elements/compounds combine to form 1

product.

• Only one product!

• Analogy: Mixing 2 or more ingredients together to get 1 cake. .

A + B AB

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

Synthesis

Example: 2 Mg + O2 2 MgO

Must crisscross to get new compound!

• Practice Problems:

• Na + F2

• B + N2

Na + F2 Na F+1 -1

Na + F2 NaF2 2

• Practice Problems:

• Na + F2

• B + N2

B + N2 B N+3 -3

B + N2 BN2 2

Decomposition Reaction

2 H2O → 2 H2 + O2

2HgO → 2 Hg + O2

A reaction in which a compound is broken down into two or more elements.

Decomposition• 1 compound is broken down into 2 or more simpler

elements/compounds.

• only one reactant

• Analogy: A couple breaks up. Or a body decompses.

AB A + B

KBr K + Br2 2 2

Decomposition

• Example

• Practice Problems:

• Na2O

• CF4

Na2O Na O

Na2O Na + O22 4

+2

Single Replacement Reaction

2 KCl + F2 → 2 KF + Cl2

Mg + 2 HCl → H2 + MgCl2

A reaction in which one element reacts with one compound to form another element and another compound.

Single Replacement

• one element replaces another in a compound– metal replaces metal (+)– nonmetal replaces nonmetal (-)

A + BC B + AC

Fe(s)+ CuSO4(aq) Cu(s)+ FeSO4(aq)

• Products:

Metal replacement:

2 Na + CuCl2 2 NaCl + Cu

Halogen replacement:

F2 + 2 KCl 2 KF + Cl2– free element must be more active (check activity series)

Br2(l)+ NaCl(aq) N.R.

Metals Nonmetals

lithium fluorine

potassium chlorine

calcium bromine

sodium iodine

magnesium oxygen

aluminum nitrogen

zinc

chromium

iron

nickel

tin

lead

hydrogen*

copper

mercury

silver

platinum

gold

Practice

• Can Al replace Li? ____

• Can Cu replace Au? ____

• Can Br replace I? ____

• Can Cl replace F? ____NO

NO

Yes

YES

• Practice Problems: • H2 + PbCl2

• Cl2 + KBr

• Zn + CuS

H2 + PbCl2 No rxn+1 -1+2

• Practice Problems: • H2 + PbCl2

• Cl2 + KBr

• Zn + CuS

Cl2 + KBr -1 -1+1

K Cl+1 -1

+ Br2

Cl2 + KBr KCl + Br222

• Practice Problems: • H2 + PbCl2

• Cl2 + KBr

• Zn + CuS

Zn + CuS +2 -2+2

ZnS+2 -2

+ Cu

Zn + CuS ZnS + Cu

Double Replacement Reaction

Pb(NO3)2 + K2CrO4 PbCrO4+ 2 KNO3

NaCl + AgNO3 AgCl + NaNO3

A reaction in which the metals present in two compounds change places to form two new compounds.

AB + CD AD + CB

Double Replacement• Ions from 2 ionic compounds switch places.

--put the inside ions together and the outside ions together

• --positive ion always goes first in the compound!

• Analogy: 2 couples are dancing, and they switch partners

Pb(NO3)2(aq)+ KI(aq) PbI2(s)+ KNO3(aq)

Double Replacement

Example:

FeCl2 + Na2CO3 2 NaCl + FeCO3

Practice #1

• Na2CO3 + Ca(NO3)2

• Na2CO3 + Ca(NO3)2

• Na2CO3 + Ca(NO3)2 NaNO3 +CaCO3

NaNO3 + CaCO3

+1 -1-2 +2

2

Practice #2

• K3PO4 + MgCl2

• K3PO4 + MgCl2

• K3PO4 + MgCl2 KCl + Mg3(PO4)2

KCl + Mg3(PO4)2

+1 -1-3 +2

2 3 6

Combustion

• When a carbon compound reacts with oxygen to make carbon dioxide and water.– Hint:

• It will always have O2 on reactant side

• It will always have CO2 and H2O on product side

• Example:CH4 + O2 → CO2 + H2O

Combustion

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

• Also known as burning; always follows the same form:• The compound always burns in oxygen gas and always

releases carbon dioxide and water.• During incomplete combustion (a limited amt. of O2),

carbon monoxide (CO) is also produced.

C & H (& sometimes O) + O2 CO2 + H2O

• Example:

• 2 C3H6 + 9 O2 6 CO2 + 6 H2O*always balance in order: C, H, O

• Practice Problems:

CH4 + O2

C6H14 + O2

CO2 + H2O22

CO2 + H2O12 142 19