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Chemical Equations

Chemical Equations. General form: Reactants Products For Example: 2Na (s) + Cl 2(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:.

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Chemical Equations

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  1. 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

  2. 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

  3. 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.

  4. 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.)

  5. 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)

  6. Don’t Forget the Diatomics! H2, N2, O2, F2, Cl2, Br2, I2 S and P can sometimes also bond with itself

  7. 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.

  8. Try Some: __C19H17NO3 + __O2 __CO2 + __H2O + __N2 __(NH4)3PO4 + __NaOH  __Na3PO4 + __NH3 + __H2O

  9. Try Some: 4C19H17NO3 + 87O2 76CO2 + 34H2O + 2N2 __(NH4)3PO4 + __NaOH  __Na3PO4 + __NH3 + __H2O

  10. Try Some: 4C19H17NO3 + 87O2 76CO2 + 34H2O + 2N2 (NH4)3PO4 + 3NaOH  Na3PO4 + 3NH3 + 3H2O

  11. Honours Class: • Sometimes you can get equations that are VERY difficult to balance • Try using the algebraic method! • see handout

  12. The Six Basic Types of Reactions: • synthesis • decomposition • single replacement • double replacement • neutralization • combustion

  13. 1) Synthesis/Combination: • General Equation: A + B  C • one new substance is made (synthesized) by combining 2 or more reactants • Example: 2H2 + O2 2H2O

  14. You Try: • H2(g) + F2(g) → • 2Al+ 3S → 2HF(g) Al2S3

  15. 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

  16. You Try: • 2 Ag2O(s) + heat → • 2 NO(g) + heat → 4 Ag(s) + O2(g) N2(g) + O2(g)

  17. 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

  18. You Try: • CuCl2(aq) + Fe(s) → • 2CaO + 2Cl2 → FeCl2(aq) + Cu(s) O2 + 2CaCl2

  19. 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

  20. You Try: • AgNO3(aq) + NaCl(aq) → • 2NaCl(aq) + H2SO4(aq) → AgCl(s) + NaNO3(aq) 2HCl(g) + Na2SO4(aq)

  21. 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

  22. You Try: • H2SO4(aq) + 2NaOH(aq) → • H3PO4(aq) + 3KOH(aq)→ Na2SO4(aq) + 2H2O(l) K3PO4(aq) + 3H2O(l)

  23. 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

  24. 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)

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