Chemical Equations General form: Reactants Products For Example: 2Na(s) + Cl2(g) 2NaCl(s) State Indicators s (solid), l (liquid), g (gas), aq (aqueous) Coefficients - from the balanced reaction Subscripts - based on the nature of the chemical

Some Vocabulary: System: Open System: Closed 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… 4 Conservation Laws: (all for closed systems) The LAW OF CONSERVATION OF… 1) MASS 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.

3) ELECTRICAL CHARGE 4) ENERGY 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.)

Writing Chemical Equations From Words 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 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 + H2O or 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) → Na2SO4(aq) + 2H2O(l) 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)