CHEMICAL EQUATIONS OF CHEMICAL REACTIONS
In order lớn write the chemical equations, you must first knowthe formulas for the materials involved. The formulas must bewritten on the proper side of the arrow - - reactants on the leftand products on the right. The order in which the reactantsand products are written does not matter, just as long as everymaterial is on the proper side. Once the materials involved inthe reaction are written correctly, DONT cảm ứng THEM. If youneed to lớn draw a box around each participant in the reaction tokeep your grubby paws off the materials, do it.
Very often you will see the descriptions of the materials inthe reaction in parentheses after the material. A gas is shown by(g).A solid material is shown by (s). Aliquid is shown by (l). Amaterial dissolved in water (an aqueous solution) is shown by(aq).An upwards pointing arrow (
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Now comes the fun part, balancing the reaction. The Law ofConservation of Mass states that in a chemical reaction there isno loss of mass. Each type of element will have the same amountbefore the reaction and after the reaction, or as reactantand product. But you cant change the materials thatparticipate in the reaction, so you must write an integercoefficient infront of (to the left of) each material in the reaction to lớn makesure every type of atom has the same number on each side ofthe reaction. Lets start with the reaction of the Haberprocess:
Nitrogen gas plus hydrogen gas under pressure & at hightemperature turn into ammonia. First write the materialscorrectly. Nitrogen và hydrogen are diatomic gases. Ammonia is abinary covalent memory item. The nitrogen andhydrogen are the reactants, & the ammonia is the product. Leaveroom for the coefficients in front of the materials.
_ N2 + _H2 _NH3
You can begin with either the nitrogen or the hydrogen. Thereare two nitrogen atoms on the left và only one on the right.In order to lớn balance the nitrogen atoms, place a 2 infront of the ammonia.
_ N2 + _H2 2NH3
There are two hydrogens on the left and six on the right. Webalance the hydrogens by placing a 3 in front of thehydrogengas.
_ N2 + 3H2 2NH3
Now go back and check to make sure everything is balanced.There are two nitrogen và six hydrogens on both sides ofthe reaction. It is balanced. There is no coefficient shown infront of the nitrogen. There is no need to lớn write ones ascoefficients. The reaction equation is:
N2 + 3H2 2NH3
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BALANCING IONIC EQUATIONS WITH POLYATOMIC IONS
Silver nitrate and calcium chloride solutions combined producea precipitate of silver chloride và leave a solution of calciumnitrate. This time we have ionic compounds in the reaction. Untilyou are sure of the compounds, you might want to lớn write theionic materials as the ions, as demonstrated here.
_ Ag+(NO3)- + _Ca2+Cl-2 _Ag+Cl- + _ Ca2+ (NO3)-2
Notice that from one side khổng lồ the other there is no change inthe nitrate ion. In this case you can count the nitrate ion as awhole rather than splitting it up into nitrogen và oxygen. Yourthoughts might go this way: How many silvers on the right?One. How many silvers on the left? One. They are the same. Howmany nitrates on the left? One. How many nitrates on theleft? One. How many nitrates on the right? Two. We need khổng lồ put acoefficient of two in front of the silver nitrate.
2 AgNO3 +_ CaCl2 _ AgCl +_ Ca (NO3)2
This changes the balance of silvers, so we have to put a twoin front of the silver chloride.
2 AgNO3 +_ CaCl2 2 AgCl +_ Ca (NO3)2
Now lets check again. Two silvers on each side. Twonitrates on each side. One calcium on each side và two chlorideson both sides. The balanced reaction is:
2 AgNO3 +CaCl2 2 AgCl +Ca (NO3)2
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BALANCING EQUATIONS WITH WATER AS A PRODUCT
Sulfuric acid và potassium hydroxide neutralize each other tomake water & potassium sulfate. Here is an acid-baseneutralization. These make a salt (Not necessarily common tablesalt.) và water. (Notice the ionic materials are written withthe ion notation so they are sure khổng lồ be right. Water and sulfuricacid are memory items và should not need lớn be written inion form, though you could write the ions khổng lồ make sure they areright.)
_ H2SO4 + _K+(OH)- _K+2(SO4)2+ + _H2O
The water is made from the hydrogen ion of the acid and thehydroxide ion of the base. Notice that it is a lot easier tounderstand how to balance the reaction if you write the water asif it were an ionic compound.
_ H2(SO4)+ _K+(OH)- _ K+2(SO4)2+ + _H+(OH)-
This is easier now because the hydrogen in the acid does notget confused with the hydrogen in the hydroxide of the base.Two hydrogens on each side. One sulfate on both sides. Twopotassiums & two hydroxides on each side.
H2(SO4)+ 2K(OH) K2(SO4) + 2 H(OH)
The reaction is now balanced.
Next is an example of having to lớn go around the equation again.Phosphoric acid and calcium hydroxide react khổng lồ make waterand calcium phosphate.
_ H3PO4 + _Ca2+(OH)-2 _ H+(OH)-+ _ Ca2+3(PO4)3-2
First put a three on the water lớn balance the hydrogen in thephosphoric acid.
_ H3PO4 + _Ca(OH)2 3H(OH) + _Ca3(PO4)2
Now put a two on the phosphoric acid to balance the phosphatefrom the calcium phosphate.
2 H3PO4 + _Ca(OH)2 3H(OH) +Ca3(PO4)2
We have changed the amount of hydrogen ion, so we will have tochange it on the right again.
2 H3PO4 + _Ca(OH)2 6H(OH) +Ca3(PO4)2
And change the coefficient in front of theCa(OH)2 to lớn match thecalcium on the right side.
2 H3PO4 + 3Ca(OH)2 6H(OH) +Ca3(PO4)2
Only now does the rest of the equation balance with sixhydrogens, six hydroxides, two phosphates, và three calciums oneach side.
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BALANCING BURNING REACTIONS
Also called COMBUSTION, most of these reactions involve burning of organic compounds with oxygen gas. Complete burning produces carbon dioxideand water from the organic compounds. Organic compounds always contain Carbon & Hydrogenelements along with other elements. Methane, an organic compoundburns in air lớn make carbon dioxide và water.
_ CH4 + _O2 _H2O + _ CO2
Easy. Put a two in front of the water lớn take care of all thehydrogens và a two in front of the oxygen. Anything you have togather (any atom that comes from two or more sources in thereactants or gets distributed to lớn two or more products) shouldbe considered last.
CH4 + _O2 2 H2O +CO2
CH4 + 2O2 2H2O + CO2
What if the oxygen does not come out right? Letsconsider the equation for the burning of butane, C4H10.
_ C4H10 + _O2 _CO2 + _ H2O
Insert the coefficients for carbon dioxide & water.
_ C4H10 + _O2 4CO2 + 5 H2O
We now have two oxygens on the left & thirteen oxygens onthe right. The real problem is that we must write the oxygenas a diatomic gas. The chemical equation is not any differentfrom an algebraic equation in that you can multiply both sidesby the same thing và not change the equation. Multiply bothsides by two khổng lồ get the following.
2 C4H10 + _O2 8CO2 + 10 H2O
Now the oxygens are easy khổng lồ balance. There are twenty-sixoxygens on the right, so the coefficient for the oxygen gas onthe left must be thirteen.
2 C4H10 + 13O2 8CO2 + 10 H2O
Now it is correctly balanced. What if you finally balanced thesame equation with:
4 C4H10 + 26O2 16CO2 + 20 H2O
6 C4H10 + 39O2 24CO2 + 30 H2O
Either equation is balanced, but not to the lowest integer.Algebraically you can divide these equations by two or three togetthe lowest integer coefficients in front of all of the materialsin the equation.
Now that we are complete pyromaniacs, lets try burningisopropyl alcohol, C3H7OH.
_ C3H7OH + _O2 _CO2 + _ H2O
First take care of the carbon và hydrogen.
_ C3H7OH + _O2 3CO2 + 4 H2O
But again we come up with an oxygen problem. The same processworks here. Multiply the whole equation (exceptoxygen) by two.
2 C3H7OH + _O2 6CO2 + 8 H2O
Now the number nine fits in the oxygen coefficient. (Doyou understand why?) The equation is balanced with sixcarbons, sixteen hydrogens, và twenty oxygens on eachside.
2 C3H7OH + 9O2 6CO2 + 8 H2O
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BALANCING BY OVERVIEW
Some equations are just mean, nasty, và rotten and defy yourefforts to lớn balance them. For some of these equations, aprocess I hotline overview is useful. Take as an example thesmelting of magnetite, an iron ore.
_ Fe3O4 + _ CO_ CO2 + _ fe
Unless you just happen to lớn hit it right, you are unlikely tobalance this equation with the trial method. (Go ahead và try itbefore you read further.)
The process overview shows that for each oxygen that themagnetite has, one carbon monoxide must turn khổng lồ carbon dioxide.The carbon monoxide & carbon dioxide must have a coefficientthat is four times the coefficient of the magnetite. Leave themagnetite coefficient and put a "4" in front of the carbonmonoxide and carbon dioxide.
_ Fe3O4 + 4 co 4 CO2 + _ sắt
The carbon và oxygen is balanced, leaving only the iron khổng lồ bebalanced.
Fe3O4 + 4 teo 4 CO2 + 3 fe
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WRITE THE FORMULA FOR EACH MATERIAL CORRECTLY ANDTHEN BALANCE THEEQUATION. THERE ARE SOME REACTIONS THAT REQUIRE COMPLETION. FOREACH REACTION TELL WHAT TYPE OF REACTION IT IS.
1. Sulfur trioxide and water combine to lớn make sulfuric acid.
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2. Lead II nitrate và sodium iodide react to make lead iodideand sodium nitrate.
3. Calcium fluoride và sulfuric acid make calcium sulfate andhydrogen fluoride (Hydrofluoric acid)
4. Calcium carbonate will come apart when you heat it to lớn leavecalcium oxide & carbon dioxide.
5. Ammonia gas when it is pressed into water will makeammonium hydroxide.
6. Sodium hydroxide neutralizes carbonic acid
7. Zinc sulfide & oxygen become zinc oxide & sulfur.
8. Lithium oxide and water make lithium hydroxide
9. Aluminum hydroxide and sulfuric acid neutralize khổng lồ makewater và aluminum sulfate.
10. Sulfur burns in oxygen to lớn make sulfur dioxide.
11. Barium hydroxide & sulfuric acid make water và bariumsulfate.
12. Aluminum sulfate & calcium hydroxide become aluminumhydroxide và calcium sulfate.
13. Copper metal và silver nitrate react to khung silver metaland copper II nitrate.
14. Sodium metal and chlorine react to lớn make sodium chloride.
15. Calcium phosphate và sulfuric acid make calcium sulfateand phosphoric acid.
16. Phosphoric acid plus sodium hydroxide.
17. Propane burns (with oxygen)
18. Zinc & copper II sulfate yield zinc sulfate & coppermetal
19. Sulfuric acid reacts with zinc
20. Calcium oxide và aluminum make aluminum oxide & calcium
21. Chlorine gas and sodium bromide yield sodium chloride andbromine
ANSWERS to lớn EQUATIONS
1. SO3 + H2O H2SO4SYNTHESIS
2. Pb(NO3)2 + 2NaI PbI2 + 2NaNO3DOUBLE REPLACEMENT (lead II iodide precipitates)
3. CaF2 + H2SO4 CaSO4 + 2 HFDOUBLE REPLACEMENT (calcium sulfate precipitates)
4. CaCO3 CaO + CO2 DECOMPOSITION
5. NH3 + H2O NH4OH SYNTHESIS
6. 2 NaOH + H2CO3 Na2CO3 + 2H2ODOUBLE REPLACEMENT OR ACID-BASE NEUTRALIZATION
7. 2 ZnS + O2 2 ZnO + 2 S SINGLE REPLACEMENT
8. Li2O + H2O 2 LiOH SYNTHESIS
9. 2 Al(OH)3 + 3 H2SO4 6 H2O + Al2(SO4)3 DOUBLE REPLACEMENT OR ACID-BASE NEUTRALIZATION
10. S + O2 SO2 SYNTHESIS
11. Ba(OH)2 + H2SO4 2 H2O + BaSO4DOUBLE REPLACEMENT OR ACID-BASE NEUTRALIZATION
12. Al2(SO4)3 + 3 Ca(OH)2 2Al(OH)3 + 3 CaSO4 DOUBLE REPLACEMENT(BOTH calcium sulfate và aluminum hydroxide areprecipitates.)