Chemical reactions - PowerPoint PPT Presentation

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Chemical reactions
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Chemical reactions

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  1. Chemical reactions Types and balancing reactions

  2. Chemical and physical changes • How do we know that a chemical reaction has happened? • Physical changes don’t change what the matter is • Chemical changes change the matter, atoms have been rearranged

  3. Chemical reactions • Reactant  product • Unbalanced chemical reactions are called skeleton equations, they are the shell of the reaction • Like a recipe without the measurements • Symbols in reactions • (s), (l), (aq), (g),  

  4. Types of reactions • Acid base • Acid + base  salt + water • HCl + NaOH  NaCl + H2O • Precipitation • A solid product is ALWAYS formed • Oxidation-reduction (red-ox) • A reactant gets reduced, the other is oxidized in the product • OIL RIG or LEO says GER both will help to remember • So how do you tell the difference? • Practice, practice, practice

  5. Acid base • Hydro-ic : will tell you acid has an H’s in it • Hydroxide will tell you base • Has OH- in it • Also called a double displacement reaction because every ion is getting a new partner

  6. Precipitation reactions • Different types of ppt reactions • Synthesis a + b  ab • Decomposition ab  a+ b • Single displacement ab + c  ac + b • Double displacement ab + cd  ad + cb • Combustion ab + O2  ___ +CO2 + H2O

  7. Red-ox reactions • Does not require oxygen to be a redox • These are reactions when oxidation number of the elements change • The elements that lose electrons are oxidized • The elements that gain electrons are reduced • LEO says GER

  8. Assigning oxidation #’s • For free elements (Ba, I2) oxidation number is 0 • Elements in group 1 are +1 (except H) • H are +1 except with hydrides (NaH) then -1 • Elements in group +2 • Halogens are -1 • Oxygen are -2 except with peroxides, then -1 • Neutral compounds are 0 • Polyatomic are the sum of all their individual

  9. Practice • Na + Cl2  NaCl • Both the Na and the Cl2 are in the free state, oxidation # 0 • The Na loses one electron and the Cl takes on one electron • Lose electron oxidize = Na • Gain electron reduce = Cl • Na reduced the Cl and Cl oxidized the Na

  10. Counting atoms • In order to complete a chemical reaction, we need to follow the conservation of mass • Mass of the reactants must equal the mass of the products • There needs to be the same amount of matter on both sides of the yield sign • So we count atoms and balance them with coefficients • Subscripts show us how many atoms belong to each compound

  11. Balancing reactions • Na + Cl2 NaCl • Do we have the same amount of mass on both sides? • Nope….1 Na , 2 Cl on reactant • 1 Na 1 Cl on product side • So we need to add coefficients to balance, CAN’T change the subscripts, ever! • 2Na +Cl2  2NaCl • Now its balanced!

  12. White board practice Balance and ID the type • Hydrogen reacts with Nitrogen to produce Nitrogen trihydride • H2 +N2  NH3 • Iron (III) oxide reacts with carbon monoxide to produce Iron and carbon dioxide • Fe2O3 + CO  Fe + CO2