Chemical Equations

• General form:

Reactants Products

• For Example:

2Na(s) + Cl2(g) 2NaCl(s)

Subscripts

- based on the nature of the chemical

Coefficients

- from the balanced reaction

State Indicators

s (solid), l (liquid),

g (gas), aq (aqueous)

Some Vocabulary:• System:

– The part of the universe being studied

• Open System:– A system where things (mass, energy) can enter and leave.

• Think beaker on a hotplate

• Closed System:– A system where NOTHING can enter or leave.

• Think Thermos

The LAW OF CONSERVATION OF…

• The mass at the beginning and the end of a chemical reaction is the same (conserved)

2) ATOMS• The total number and type of atoms in a

closed system does not change during a chemical reaction.

4 Conservation Laws: (all for closed systems)

1) MASS

3) ELECTRICAL CHARGE

• The total electrical charge in a closed system does not change during a chemical reaction.

4) ENERGY• The total energy in a closed system does not

change during a chemical reaction. (The amounts of the various types of energy may change, but the total remains constant.)

• Hydrochloric acid reacts with calcium carbonate crystals, producing aqueous calcium chloride, gaseous carbon dioxide and, liquid water.

• Gaseous xenon hexafluoride reacts violently with water to form solid xenon trioxide and gaseous hydrogen fluoride

Writing Chemical Equations From Words

2HCl(aq) + CaCO3(s) CaCl2(aq) + CO2(g) + H2O(l)

XeF6(g) + 3H2O(g) XeO3(s) + 6HF(g)

Don’t Forget the Diatomics!H2, N2, O2, F2, Cl2, Br2, I2

S and P can sometimes also bond with itself

Some tips for Balancing Reactions…

• Start with any metals! • Then, balance anything besides H and O.

– H and O are often found several times in a reaction and usually cannot be balanced until everything else is first.

• Try to balance entire polyatomic groups (SO4, NO3, PO4, etc.), if possible.– To do this, the polyatomic ion would have to be found

on both sides of the reaction

• Diatomics can cause problems. If you get a fraction (eg. ½), multiply the equation by a whole number (eg. 2) which eliminates the fraction.

Try Some:

__C19H17NO3 + __O2 __CO2 + __H2O + __N2

__(NH4)3PO4 + __NaOH __Na3PO4 + __NH3 + __H2O

Try Some:

4C19H17NO3 + 87O2 76CO2 + 34H2O + 2N2

__(NH4)3PO4 + __NaOH __Na3PO4 + __NH3 + __H2O

Try Some:

4C19H17NO3 + 87O2 76CO2 + 34H2O + 2N2

(NH4)3PO4 + 3NaOH Na3PO4 + 3NH3 + 3H2O

Honours Class:

• Sometimes you can get equations that are VERY difficult to balance

• Try using the algebraic method!– see handout

The Six Basic Types of Reactions:

• synthesis

• decomposition

• single replacement

• double replacement

• neutralization

• combustion

1) Synthesis/Combination:

• General Equation:

A + B C

• one new substance is made (synthesized) by combining 2 or more reactants

• Example: 2H2 + O2 2H2O

You Try:

• H2(g) + F2(g) →

• 2Al + 3S →

2HF(g)

Al2S3

2) Decomposition:

• General Equation:

A B + C• a reactant breaks down to form two or more

products (decomposes)• reverse of synthesis reaction• heat or light is generally added as a catalyst for

this reaction– (Note: catalyst = substance that speeds up a chemical

reaction)

• Example: 2NH3 N2 + 3H2

You Try:

• 2 Ag2O(s) + heat →

• 2 NO(g) + heat →

4 Ag(s) + O2(g)

N2(g) + O2(g)

3) Single Replacement:

• General Equation: A + BC B + AC

• either the cations or the anions in the reactants “switch places” to form new products

• one element will be independent of other elements in the reactants and in the products

• Example: CuSO4 + Fe FeSO4 + Cu

You Try:

• CuCl2(aq) + Fe(s) →

• 2CaO + 2Cl2 →

FeCl2(aq) + Cu(s)

O2 + 2CaCl2

4) Double Replacement:

• General Equation:

AB + CD AD + CB

• both the cations and the anions in the reactants “switch places” to form new products

• Example: LiBr + NaF LiF + NaBr

You Try:

• AgNO3(aq) + NaCl(aq) →

• 2NaCl(aq) + H2SO4(aq) →

AgCl(s) + NaNO3(aq)

2HCl(g) + Na2SO4(aq)

5) Neutralization:

• General Equation:

Acid + Base Salt + H2Oor

HX + MOH MX + H2O

• special case of a double replacement reaction

• note a salt (ionic compound) and water are produced

• Example: 2HCl + Ca(OH)2 CaCl2 + 2H2O

You Try:

• H2SO4(aq) + 2NaOH(aq) →

• H3PO4(aq) + 3KOH(aq) →

Na2SO4(aq) + 2H2O(l)

K3PO4(aq) + 3H2O(l)

6) Combustion:

• General Equation:

Hydrocarbon + O2 CO2 + H2O

• note: oxygen is a reactant, and carbon dioxide and water are always produced

• Example: 2C2H6 + 7O2 4CO2 + 6H2O

More Combustion:

• Sometimes other elements are involved in the hydrocarbon (we will only look at when oxygen or sulphur are included)

• Example:C5H12O2(l) + 7O2(g) → 5CO2(g) + 6H2O(l)

C5H12S(l) + 9O2(g) → 5CO2(g) + 6H2O(l) + SO2(g)