BALANCING CHEMICAL EQUATIONS - Notre dame Chemistry



BALANCING CHEMICAL EQUATIONS [9.1]

The total number of each element must be the same on each side of the arrow. Coefficients (big numbers in front of the formulas) may be added or changed. Subscripts (little numbers in the middle or at the end of the formulas) may NOT be added or changed.

Step 1: Count the amount of each element on each side of the arrow. Write the number in the space below the equation. If it is the same element but in two different compounds, put the total amount in the blank.

Step 2: If the numbers do not match, figure out what Coefficient must be added to make the numbers match. A coefficient will MULTIPLY all the elements in the formula by its amount. Remember, same elements in different compounds are added to give the total.

Step 3: Write the coefficients correctly in the spaces in the chemical equation. If the coefficient is “1” it is understood and does not need to be shown.

Step 4: Double check to make sure the total number of each element is the same on both sides.

1. ______ C2H2 + _______ O2 -----> _______ CO2 + _______ H2O

____ C ____

____ H ____

____ O ____

2. ____ Na3PO4 + _____ Ba(NO3)2 -----> _____ Ba3(PO4)2 + ______ NaNO3

____ Na ____

____ Ba ____

____ NO3 ____

____ PO4 ____

3. _____ H3AsO4 + ______ Pb(NO3)2 ----> ______ HNO3 + ______ PbHAsO4

____ H ____

____ As ____

____ Pb ____

____ N ____

____ O ____

4. ______ KNO3 ----> _______ KNO2 + _______O2

____ K ____

____ N ____

____ O ____

In “real” chemical equations, there are no blanks. Try to do these without the blanks, or make them on your own.

5. C4H8 + O2 ----> CO2 + H2O

6. Hg + O2 ----> HgO

7. AgNO3 + NaCl ----> AgCl + NaNO3

8. P4 + O2 → P2O5

9. Fe + H2O→ Fe3O4 + H2

Types of Chemical Equations [9.2]

In a chemical equation there are always something that reacts (written on the left) to produce something new (written on the right).

There are four main types of chemical equations.

Addition (a.k.a. Combination): 2 chemicals react to produce one new chemical

Like peanut butter and jelly combine to make a sandwich

Solid calcium oxide and sulfur dioxide gas combine to produce solid calcium sulfite.

Decomposition: 1 chemical is broken into 2 new chemicals

Like taking an oreo cookie and separating it into two parts

Calcium carbonate solid is broken down into calcium oxide solid and carbon dioxide gas.

Combustion (a.k.a. Burning): A chemical containing carbon and hydrogen (known as a hydrocarbon) is reacted with oxygen gas (O2) to make carbon dioxide gas (CO2) and water vapor (this is water in the form of a gas).

butane liquid (tetracarbon decahydride), when burned reacts with oxygen to produce carbon dioxide gas and water vapor.

Replacement: There are two kinds of replacement, single and double. These are sometimes called displacement reactions. In the single, 1 element replaces something in a compound to produce a new compound and a different single element. In the double, 2 chemicals react to produce 2 different chemicals: A double replacement that involves a strong acid and a strong base is called a neutralization.

A piece of copper metal is dropped in a solution of silver nitrate.

A solution of silver nitrate is mixed with salt water

2 on the reactant side (left) 1 on the product side (right) COMBINATION

1 on the reactant side (left) 2 on the product side (right) DECOMPOSITION

1 of the reactants is O2(g) the products are H2O(l) and CO2(g) COMBUSTION

2 compounds on the reactant side 2 different compounds on the product side

DOUBLE REPLACEMENT

1 single element and 1 compound on the reactant side a different single element and compound on the product side SINGLE REPLACEMENT

1. K(s) + H2O(l) -----> KOH(aq) + H2(g) ________________________

2. KNO3(s) ----> KNO2(s) + O2(g) ________________________

3. C4H8(l) + O2(g) ----> CO2(g) + H2O(l) ________________________

4. Hg(l) + O2(g) ----> HgO(l) ________________________

5. AgNO3(s) + BaCl2 ----> AgCl(s) + Ba(NO3)2(aq) ____________________

6. H2(g) + O2(g) → H2O(l) ________________________

7. H2S(g) + Cl2(g) ---> S8(s) + HCl(g) ________________________

8. FeCl3(aq) + NH4OH(aq) ---> Fe(OH)3(s) + NH4Cl(aq)____________________

9. NH3(g) → H2(g) + N2(g) ________________________

10. CH4 (g) + O2 (g) ( CO2 (g) + H2O (g) ________________________

11. Fe (s) + CuNO3 (aq) ( Cu (s) + Fe(NO3)2 (aq) ________________________

12. CO (g) + O2 (g) ( CO2 (g) ________________________

Write the following chemical equations. Make sure to use the little parentheses to indicate if it is a solid, liquid, gas or aqueous (dissolved in water). Balance and ID

1. Sulfur dioxide gas reacts with oxygen gas to make sulfur trioxide gas.

2. Calcium carbonate solid is heated to produce calcium oxide solid and carbon dioxide gas.

3. Benzene (hexacarbon hexahydride) and oxygen are burned. (The products are not told but you can figure them out if you know what type of reaction is a.k.a. burning)

4. Solid zinc is combined with oxygen gas to make zinc oxide solid.

5. Silver and dihydrogen monosulfide react in a single displacement reaction.

6. A solution lead(II) nitrate and a solution of potassium sulfate react by double displacement to form a precipitate.

7. Aluminum reacts with iron (II) nitrate to form aluminum nitrate and iron.

Predicting Precipitates Practice [9.3]

1. Use solubility rules to determine if a precipitate will form. MEMORIZE:

a) ALL ALKALI METALS ARE SOLUBLE (won't make a solid)

b) THE FOLLOWING POLYATOMIC IONS ARE SOLUBLE (won't make a solid)

NITRATE AMMONIUM ACETATE

(NO3-) (NH4+) (CH3COO-)

2. Eliminate the spectator ions (look at (a) and (b) above:

3. If a precipitate is predicted, write the balanced net ionic equation with states [(s) etc. ]

Note: If no precipitate forms write: No reaction

Example:

potassium carbonate + iron(III) chloride

Eliminate the spectator ions: Potassium is in group 1 so it is eliminated.

Chloride won’t have a partner, so it is eliminated.

equation: 2Fe3+(aq) + 3CO32-(aq) Fe2(CO3)3(s)

a) write the ions first b) then swap charges to write the formula of the product

c) put coefficients in front of reactants to balance d) don’t forget the states!

a) magnesium nitrate + zinc sulfate

b) sodium acetate + lithium iodide

c) rubidium phosphate + copper(II) sulfide

d) ammonium oxide + manganese(IV) chloride

e) nickel(II) nitrate + iron(II) acetate

f) iron(III) chlorate + sodium hydroxide

Producing Gases and Liquid [9.3]

H2CO3 readily decomposes into H2O and CO2 gas,

H2CO3(aq) → H2O(l) + CO2(g)

So, any solution reaction that leads to the production of H2CO3, such as

HCl(aq) + NaHCO3(aq) → NaCl(aq) + H2CO3(aq)

will ultimately lead to the production of H2O and CO2 gas as the H2CO3 decomposes, giving us a new equation:

HCl(aq) + NaHCO3(aq) →  H2O(l) + CO2(g) + NaCl(aq) 

MEMORIZE: CARBONATE (CO32-) and an ACID will make WATER, CARBON DIOXIDE + “SALT”

g) calcium carbonate + hydrosulfuric acid

h) lithium carbonate + phosphoric acid

i) ammonium carbonate + nitrous acid

MEMORIZE: AN ACID AND A STRONG BASE (OH-) will make WATER + “SALT”

Hydroiodic acid reacts with sodium hydroxide to produce water and sodium iodide

HI(aq)  + NaOH(aq)  ( H2O(l)  + NaI(aq) 

j) hydrobromic acid and barium hydroxide

k) zinc hydroxide and nitric acid

Practice: This is an assortment of reactions that may produce a solid (precipitate), liquid (water), or gas (CO2)

Write and balance the chemical reaction. Don’t forget the states! If all species stay aqueous, write: No Rxn.

Assume all species start as aqueous solutions

1. aluminum hydroxide and hydrochloric acid

2. nitric acid + sodium carbonate

3. chromium(III) nitrate + iron(II) sulfide

 

4. potassium phosphate + ammonium nitrate

5. nickel(III) nitrate + potassium chromate

6. rubidium carbonate + sulfuric acid

7. scandium hydroxide + sulfurous acid

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When you see a polyatomic ion represented on both sides of the equation, keep it together as a polyatomic when balancing.

Distribute the 2 that is outside the parentheses

Save the oxygen for the end

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