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Understanding Chemical Reactions: Types, Balancing, and Changes

This guide explores the fundamentals of chemical reactions, covering definitions, types, and balancing methods. Learn how to identify chemical and physical changes, understand reactants and products, and recognize the significance of skeleton equations. We delve into various reactions, including acid-base, precipitation, and redox processes, while emphasizing the importance of mass conservation in balancing equations. With practical examples and tips, you’ll gain the skills needed to analyze and balance chemical reactions confidently.

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Understanding Chemical Reactions: Types, Balancing, and Changes

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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

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