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Describing Chemical Reactions

Describing Chemical Reactions. http://www.youtube.com/watch?v=F54rqDh2mWA. Chemical Change v. Physical Change. Chemical Change Break or form chemical bonds Molecular formulas of the products are NOT exactly the same as the reactants Example:

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Describing Chemical Reactions

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  1. Describing Chemical Reactions http://www.youtube.com/watch?v=F54rqDh2mWA

  2. Chemical Change v. Physical Change Chemical Change • Break or form chemical bonds • Molecular formulas of the products are NOT exactly the same as the reactants Example: 2NaCl (aq) + 2H2O (l)→ 2NaOH (aq) + Cl2(g) + H2(g)

  3. Chemical Change v. Physical Change Physical Change • DO NOT break or form chemical bonds • Molecular formulas of the products ARE exactly the same as the reactants • Change in state (phase) of matter • Change in solution

  4. Chemical Change v. Physical Change Physical Change Examples: (s)→(l) or (l)→ (g) or (s)→ (aq) Br2(l) → Br2 (g) NaCl(s)→ NaCl(aq) H2O (l)→ H2O (s) C6H12O6 (aq) → C6H12O6(s)

  5. Writing Chemical Equations • used to convey as much info. as possible about what happens in a chemical reaction

  6. Word Equations • write out what chemicals are reacting • hydrogen peroxide → water + oxygen • hydrogen + oxygen → water • Chemical Equations • show the chemical formulas of the chemicals reacting • H2O2 (aq) → H2O(l) + O2(g) • H2(g) + O2(g) → H2O (l) • (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous solution {see Table 11.1 in text} • the above are often referred to as skeletal equations because they are not mathematically balanced

  7. MnO4 • a catalyst is a substance that speeds up the reaction but is not used up in the reaction • H2(g) + O2(g) H2O (l)

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

  9. this is NOT balanced

  10. A solution of sodium iodide is added to a solution of potassium nitrate to make a potassium iodide precipitateand a sodium nitrate solution. • NaI(aq) + KNO3(aq)  KI (s) + NaNO3(aq) • 2. Magnesium metal burns in oxygen gas with a bright white light to make a white powder called magnesium oxide. • Mg (s) + O2 (g) MgO (s) + heat • 2Mg (s) + O2 (g) 2MgO (s) + heat • 3. Gaseous hydrogen (dihydride) and gaseous oxygen (dioxide) react explosively to form water vapor. • H2 (g) + O2 (g)  H2O (g) + heat • 2H2(g) + O2(g) 2H2O (g) + heat

  11. ?

  12. How about these? • Na2SiO3 + HF  H2SiF6 + NaF + H2O • Na2SiO3 + 8HF  H2SiF6 + 2NaF + 3H2O • 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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