Just a Small Note on Nomenclature Before We Begin Chemical Reactions

Regents Chemistry

Mrs. Ermann

Chemical Reactions

(from: http://crescentok.com/staff/jaskew/isr/chemistry/class11.htm)

Just a small note on nomenclature before we begin chemical reactions:

Some elements are SO REACTIVE that they will form DIATOMIC ELEMENTS with each other. For example, fluorine will immediately combine with another fluorine to become stable (achieve an octet). Therefore, the follow will ALWAYS be diatomic IF THEY ARE NOT COMBINED IN A COMPOUND:

They are:

Element / Diatomic Formula / How to remember:
Iodine / I2 / I
Bromine / Br2 / Brought
Chlorine / Cl2 / Chlorine
Fluorine / F2 / For
Oxygen / O2 / Our
Nitrogen / N2 / New
Hydrogen / H2 / Hottub!!!

Chemical reactionsare processes in which substances change into other substances.

INDICATIONS A CHEMICAL REACTION HAS OCCURRED

A chemical reaction takes place if one or more of these occur:

1. Color changes- Different combinations of compounds reflect light differently. A color change indicates a change in compounds when reactants change into products.

2. Heat is given off or taken in. These are:

· Exothermic – heat is given off.

· Endothermic – heat is taken in (and it feels cold).

3. Gas is produced- Whenever a gaseous product forms in a liquid solution, bubbles can be seen.

4. Precipitate forms- Precipitates are insoluble products formed by a reaction taking place in a liquid solution. This insoluble product will eventually settle to the bottom, but might immediately appear by turning the clear solution cloudy.

5. Light is given off - for example, the flash of an explosion.

6. A new odor is given off.

CHEMICAL REACTION EQUATIONS

There are two parts to each chemical equation:

1. Reactants – these are the elements/compounds that are going to react and are located on the left side of the equation.

2. Products – these are the new elements/compounds that are made after the reaction has occurred and are on the right side of the equation.

3. In a chemical equation, the + sign is read as "reacts with" and the arrow is read as "produces".

Example:

THE FIVE BASIC TYPES OF REACTIONS:

Most chemical reactions can be placed into one of five basic types:
1. Decomposition Reactions

· A compound breaks into its component parts.

· compound → element + element

· EXAMPLE: 2H2O(l) → 2H2(g) + O2(g) (water decomposes into hydrogen and oxygen)

2. Synthesis Reactions

· Elements are joined together.

· element + element → compound

· EXAMPLE: 2H2(g) + O2(g)→ 2H2O(l) (Hydrogen and oxygen combine to form water)

3. Single Displacement Reactions

· A single element replaces an element in a compound.

· element + compound → element + compound

· There are two different types of single displacement reactions:

1. Metal displacement: a more active metal replaces a less active metal in a compound.

2. Halogen Replacement: a more reactive HALOGEN (Group 17) replaces a less active halogen in a compound.

· EXAMPLE: Since Iodine is lower on Table J than Fluorine, Fluorine will replace Iodine in the sodium iodide compound.

NaI(aq) + F2(g) → 2NaF(aq) + I2(aq)

4. Double Displacement Reactions

· An element from each of two compounds switch places.

· compound + compound → compound + compound

· 3NaOH(aq) + AlCl3(aq) → 3NaCl(aq) + Al(OH)3 (s)

5. Combustion Reactions

· Ahydrocarbon(a compound containing only carbon and hydrogen) combines with oxygen.

· The products of combustion arealways carbon dioxide and water.

· hydrocarbon + oxygen → carbon dioxide + water

· CH4+ 2O2→ CO2+ 2H2O (methane gas reacts with oxygen to produce water and carbon dioxide)

Thephysical stateof each substance in a reaction may be shown in an equation by placing the following symbols to the right of the formula:

· (g) for gas

· (l) for liquid

· (s) for solid

· (aq) for aqueous (water) solution - the solid ionic compound is dissolved in water

Summary:

Identify the following chemical reactions as one of the five types of reactions.

1. / 1) Ca(s) + 2CuCl(aq) ® CaCl2(aq) + 2Cu(g)
2. / 2) 2 Al(OH)3(aq) + 3 Sr(s) ® 3 Sr(OH)2(aq) + 2 Al(s)
3. / 3) Ni(NO3)2(aq) + Na2CO3(aq) ® NiCO3(s) + 2 NaNO3(aq)
4. / 4) 8 Cu(s) + S8(s) ® 8CuS(s)
5. / 5) 2 NO + O2 ® 2 NO2
6. / 6) 3Na2Cr2O7(aq) + 2 AlCl3(aq) ® 6NaCl(aq) + Al2(Cr2O7)3(aq)
7. / 7) 2 Hg(NO3)2(s) ® 2 HgO(s) + 4 NO2(g) + O2(g)
8. / 8) U(s) + 3 F2(g) ® UF6(s)
9. / 9) RhO3(s) ® RhO(s) + O2(g)
10. / 10) 2 Al(s) + 3 Cu(NO3)2(aq) ® 2 Al(NO3)3(aq) + 3 Cu(s)
11. / 11) Mg(s) + 2 HF(aq) ® MgF2(aq) + H2(g)
12. / 12) 2 NaNO3(s) ® 2 NaNO2(s) + O2(g)
13. / 13) Pb(NO3)2(aq) + 2 KI(aq) ® PbI2(s) + 2 KNO3(aq)
14. / 14) SO3(g) + H2O(l) ® H2SO4(aq)
15. / 15) Pb(NO3)2(aq) + H3AsO4(aq) ® PbHAsO4(s) + 2 HNO3(aq)
16. / 16) 2 Al(s) + 3 Fe(NO3)2(aq) ® 2 Al(NO3)3(aq) + 3 Fe(s)

Counting Atoms in Chemical Formulas

1. Chemical formulas can have three components.

a) The ______which are represented by a single uppercase letter, or represented by an uppercase letter followed by a lowercase letter. This tells you the types of elements in the compound.

b) The ______which are numbers that are found on the lower ______- hand side of each element symbol. This tells you the number of ______of this element in the molecule. If an element symbol has no subscript next to it, then this indicates that there is only ______atom of this element in the molecule.

c) The ______which surround some groups of atoms indicate that the numbers of all of the atoms inside the bracket need to be ______by the ______on the outside of the bracket found on the lower ______- hand side of that bracket.

2. Record the number of each atom in each molecule, then record the total number of atoms in the molecule:

1) NaOH / 2) HNO3 / 3) Li2O
Element / # of Atoms / Element / # of Atoms / Element / # of Atoms
Total / Total / Total
4) Li2SO4 / 5) NH4Cl / 6) CaClO3
Element / # of Atoms / Element / # of Atoms / Element / # of Atoms
Total / Total / Total
7) H2COCH2 / 8) Mg(OH)2 / 9) Al(OH)3
Element / # of Atoms / Element / # of Atoms / Element / # of Atoms
Total / Total / Total
10) NH4C2H3O2 / 11) NaC2H3O2 / 12) (NH4)3PO4
Element / # of Atoms / Element / # of Atoms / Element / # of Atoms
Total / Total / Total
13) Ca3(PO4)2 / 14) Fe2(CO3)3 / 15) Al2(SO3)3
Element / # of Atoms / Element / # of Atoms / Element / # of Atoms
Total / Total / Total

Balancing Chemical Reactions

A chemical equation must have the same number of atoms of each element on both sides of the arrow. When this condition is met, the equation is said to bebalanced according to the Law of Conservation of Mass: themassof any one element at the beginning of a reaction will equal themassof that element at the end of the reaction.

To balance a chemical reaction, coefficient may need to be used. The coefficients indicate the number of that compound is needed.

Coefficients of 1 are never written - they are understood.

To count atoms, when a coefficient is present:

For example: 2Al2(SO4)3

· For Al - coefficient of 2, times subscript of 2 = 4 aluminum atoms

· For S - there are 3 sulfurs present (indicated on the outside of the parenthesis), then multiply 3 by 2 (the coefficient), so there are 6 sulfurs present.

· For O - there are 12 oxygens present (subscript inside parenthesis of 4, times subscript outside parenthesis of 3). Multiply 12 times the coefficient of 2 = 24 oxygen atoms

HOW TO BALANCE CHEMICAL REACTIONS

We will use the following equation:

H2 + O2 → H2O

1. Make a chart showing the number of atoms on the reactant side and the number of atoms on the product side:

Element / Reactant
side / Product
side
H / 2 / 2
O / 2 / 1

When the reaction is balanced, the numbers in the Reactant and Product side will be the same.

2. The oxygen is not the same as the hydrogen on the product side, so we need to add the coefficient of 2 in front of the water molecule on the product side.

H2 + O2 → 2H2O

Recount the atoms on each side.

Element / Reactant
side / Product
side
H / 2 / 2 4
O / 2 / 1 2

3. There are now more hydrogens on the product side than on the reactant side. To fix this, place a coefficient in front of the hydrogen on the reactant side.

2H2 + O2 → 2H2O

Recount the atoms on each side:

Element / Reactant
side / Product
side
H / 2 4 / 2 4
O / 2 / 1 2

Now both sides have the same number of atoms, so the reaction is balanced.

IMPORTANT: NEVER change subscripts to balance equations.

Balancing compounds with polyatomic ions

When a polyatomic ion appears on the product and reactant side, keep those atoms together as a group. Do not break them apart into their atoms.

Example: Balance the following equation:

NaNO3 + MgSO4 → Na2SO4 + Mg(NO3)2

Reactant / Product
Na / 1 / 2
NO3 / 1 / 2
Mg / 1 / 1
SO4 / 1 / 1

Add coefficients to balance: 2NaNO3 + Mg(SO4)2 → Na2SO4 + Mg(NO3)2

Reactant / Product
Na / 2 / 2
NO3 / 2 / 2
Mg / 1 / 1
SO4 / 1 / 1

The equation is balanced.

1. Balance the following equations. Make sure that you use the lowest possible whole number coefficients. Check that there are the same number of atoms of each element on both sides of the equation.

Example

_3__C + _4__H2 → __C3H8 (Note there are 3 carbon atoms and 8 hydrogen atoms on each side. No need to write “1” as a coefficient in front of C3H8)

___H2O + ___O2 → ___H2O2

___N2 + ___H2 → ___NH3

___P + ___O2 → ___P2O5

___CaO + ___MnI4 → ___MnO2 + ___CaI2

___Ag2O → ___Ag + ___O2

___NaI + ___Pb(SO4)2 → ___ PbI4 + ___Na2SO4

___HNO3 + ___Mg(OH)2 → ___H2O + ___Mg(NO3)2

___CF4 + ___Br2 → ___CBr4 + ___F2

___NaBr + ___Ca(OH)2 → ___CaBr2 + ___NaOH

2. Balance the following equations. Make sure that you use the lowest possible whole number coefficients. ALSO note the type of reaction to the right of the equation.

Example:

__2_KClO3 → __2_KCl + _3__O2 = Decomposition
___H2 + ___O2 → ___H2O ______

___NaCl + ___F2 → ___NaF + ___Cl2 ______

___AlBr3 + ___K2SO4 → ___KBr + ___Al2(SO4)3 ______

___NaBr + ___CaF2 → ___NaF + ___CaBr2 ______

___FeCl3 + ___NaOH → ___Fe(OH)3 + ___NaCl ______

___Na + ___H2O → ___NaOH + ___H2 ______

___H3PO4 + ___NaBr → ___HBr + ___Na3PO4 ______

___K + ___MgBr2 → ___KBr + ___Mg ______

___Fe(OH)3 → ___Fe2O3 + ___H2O ______

___H2SO4 + ___NaNO2 → ___HNO2 + ___Na2SO4______

___AlBr3 + K2SO4 → ____KBr + Al2(SO4)3 ______

___AgNO3 + MgCl2 → AgCl + Mg(NO3)3 ______

___HCl + CaCO3 → CaCl2 + H2CO3 ______
___FeCl3 + NH4OH → NH4Cl + Fe(OH)3 ______
Bi(NO3)3 + H2SO4 → Bi2(SO4)3 + HNO3 ______

Directions:1. Write the correct chemical formulas showing all appropriate symbols (aq, s, l, g)

2. Name the type of reaction.

3. Balance the equation.

ALL RULES OF NOMENCLATURE APPLY! Write out the ions and criss-cross!!!!!

REMEMBER TO USE DIATOMIC ELEMENTS WHEN NEEDED!!!!

Solid aluminum reacts with oxygen gas to form solid aluminum oxide.
Synthesis
Al+3O-2
4Al(s) + 3O2(g) → 2Al2O3(s)
Solid sodium oxide reacts with liquid water to form solid sodium hydroxide.
Aqueous sulfuric acid and aqueous sodium hydroxide react to form aqueous sodium sulfate and water.
Solid aluminum reacts with aqueous zinc chloride to produce solid zinc metal and aqueous aluminum chloride.
Solid zinc reacts with aqueous sulfuric acid to form aqueous zinc sulfate and hydrogen gas.
Aqueous potassium bromide decomposes to form potassium metal and bromine liquid.
Solid magnesium nitride and water combine to form magnesium hydroxide and aqueous ammonia.
At high temperatures, solid aluminum oxide decomposes into solid aluminum metal and oxygen gas.
Solid calcium reacts with aqueous aluminum chloride to form aqueous calcium chloride and solid aluminum metal.
Aqueous Iron(III)Chloride reacts with aqueous Sodium hydroxide to form aqueous Iron(III)hydroxide and aqueous sodium chloride
Solid potassium metal reacts with aqueous magnesium bromide to form aqueous potassium bromide and solid magnesium metal.
Aqueous Copper(II)nitrate reacts with aqueous sodium hydroxide to form solid copper(II)hydroxide and aqueous sodium nitrate
Aqueous nickel(II)bromide reacts with aqueous sodium carbonate to form solid nickel(II)carbonate and aqueous sodium bromide.
Aqueous Cadmium(III)Sulfate reacts with aqueous potassium hydroxide to form solid cadmium(II)hydroxide and aqueous potassium sulfate.

Hydrocarbon Combustion Reactions

Hydrocarbon combustion reactions are any chemical reaction where the reactants are a hydrocarbon (CxHy) and oxygen, which react to form carbon dioxide and gaseous water. THE PRODUCTS ARE ALWAYS CARBON DIOXIDE AND GASEOUS WATER! You may typically think of a combustion reaction is one that “burns.”

All hydrocarbon reactions have the following chemical equation:

CxHy + O2(g) → CO2(g) + H2O(g)

(CxHy stands for any hydrocarbon – the subscripts will be different for each type of hydrocarbon).

A familiar combustion reaction is the burning of propane in a home bar-b-que. Propane gas (C3H8) will burn in the presence of oxygen (O2 from the air) to produce carbon dioxide and water.