Post on 31-Dec-2015
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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)