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Describing Chemical Reactions

Describing Chemical Reactions. A chemical reaction is the process of breaking of chemical bonds (ionic or covalent) in one or more substances, and the reforming of new bonds to create new substances indicators of chemical change are: f ormation of new gas

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Describing Chemical Reactions

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  1. Describing Chemical Reactions

  2. A chemical reaction is the process of breaking of chemical bonds (ionic or covalent) in one or more substances, and the reforming of new bonds to create new substances • indicators of chemical change are: • formation of new gas • formation of new precipitate (solid) • release of energy (heat or light) • color change

  3. energy is stored in the ionic and covalent bonds of molecules • exothermic reaction– energy is released (burning) • endothermic reaction– energy is absorbed (cold packs)

  4. some important chemical reactions • burning of fossil fuels • photosynthesis • rusting of metals

  5. Conservation of mass • matter cannot be created nor destroyed in chemical reactions

  6. chemical equations convey as much info. as possible about what happens in a chemical reaction during a chemical change

  7. Balancing Chemical Equations • each side of the equation must have the same number of atoms of each elements • bicycle example • skeletal equation • frame + wheel + handlebar + pedal → bike • balanced equation • frame + 2 wheels + handlebar + 2 pedals → bike • tricycle example • skeletal equation • frame + wheels + handlebar + bell → tricycle • balanced equation • frame + 3 wheels + handlebar + bell → tricycle

  8. NOT BALANCED!

  9. this is NOT balanced

  10. How about these? • ?KCl + ? H2SO4 ? HCl + ? K2SO4 • 2KCl + H2SO4 2HCl + K2SO4 • NaCl(aq) + AgNO3(aq)  AgCl(s) + NaNO3(aq) • balanced • Al(s) + O2(g)  Al2O3(s) • 4Al(s) + 3O2(g)  2Al2O3(s)

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