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Writing Chemical Equations

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  1. Writing Chemical Equations

  2. Parts of a Reaction • Reactants • The starting materials in a chemical reaction • Products • The substances that are formed in a chemical reaction

  3. Parts of a Reaction • A chemical equation shows how atoms are rearranged during a reaction • Reactants appear on the LEFT • Products appear on the RIGHT • An arrow separates the reactants from the products () Reactants  Products

  4. Special Notations • Descriptions of the compounds appear as subscripts after the compound. • Gas: (g) • Liquid: (l) • Solid: (s) • Aqueous: Dissolved in water (aq)

  5. Special Notations • Special conditions appear with the arrow. • Heat: Heat is added to make the reaction happen • D • Catalyst: A catalyst is added in order for the reaction to happen – The compound is listed • Pt

  6. Writing a Chemical Equation Potassium oxide (K2O) and water react to form potassium hydroxide (KOH). • Reactants: K2O, H2O • Products: KOH K2O + H2O  KOH

  7. Writing a Chemical Equation Aluminum and iron oxide (FeO) react to form aluminum oxide (Al2O3) and iron. • Reactants: Al, FeO • Products: Al2O3, Fe Al + FeO  Al2O3 + Fe

  8. Writing a Chemical Equation Silicon dioxide (SiO2) and hydrogen fluoride (HF) react to form silicon tetrafluoride (SiF4) and water. • Reactants: SiO2, HF • Products: SiF4, H2O SiO2 + HF  SiF4 + H2O

  9. Writing a Chemical Equation Solid sodium carbonate (Na2CO3) and aqueous hydrochloric acid (HCl) react to form carbon dioxide gas (CO2), liquid water, and aqueous sodium chloride (NaCl) • Reactants: Na2CO3(s), HCl(aq) • Products: CO2(g), H2O(l), NaCl(aq) Na2CO3(s) + HCl(aq) CO2(g) + H2O(l) + NaCl(aq)

  10. Writing a Chemical Equation Heating solid sodium nitrate (NaNO3) results in solid sodium nitrite (NaNO2) and gaseous oxygen (O2) • Reactants: NaNO3(s) • Products: NaNO2(s), O2(g) • Special Conditions: Heat NaNO3(s)NaNO2(s) + O2(g) D

  11. Writing a Chemical Equation Aqueous hydrogen peroxide (H2O2) reacts to form liquid water (H2O) and oxygen gas (O2) in the presence of a platinum catalyst (Pt). • Reactants: H2O2(aq) • Products: H2O (l), O2(g) • Special Conditions: Platinum Catalyst H2O2(aq)H2O (l)+ O2(g) Pt

  12. Balancing an Equation • In a chemical reaction, atoms are rearranged, but they cannot be destroyed or changed. • If an atom appears on the left side of the reaction, it must appear on the right side.

  13. Balancing an Equation K2O + H2O  KOH • In the reaction above, there are unequal numbers of atoms on either side • Potassium (K): 2 atoms on the left, 1 atom on the right • Oxygen (O): 2 total on the left, 1 atom on the right • Hydrogen (H): 2 atoms on the left, 1 atom on the right.

  14. Balancing an Equation K2O + H2O  KOH • The reaction must be modified in order to make the atoms equal • We CANNOT add subscripts to KOH, because that would change the compound. • Instead, we add coefficients in front of compounds.

  15. Balancing an Equation Determine how many of each atom are present. ___ K2O + ___ H2O  ___ KOH K O K H O H K O H K: 2 K: 1 H: 2 H: 1 O: 2 O: 1

  16. Balancing an Equation There are different numbers of atoms on both sides. In order to match them up, we can add more compounds, but not atoms alone. ___ K2O + ___ H2O  ___ KOH K O K H O H K O H K O H K: 2 K: 1 H: 2 H: 1 O: 2 O: 1

  17. Balancing an Equation The number of each atom in the compound changes. ___ K2O + ___ H2O  ___ KOH K O K H O H K O H K O H 2 K: 2 K: 1 H: 2 H: 1 O: 2 O: 1 2 2

  18. Balancing an Equation Now that all the atoms are balanced, we can add up all the compounds. 1 K2O + 1 H2O  2 KOH This is called a coefficient K O K H O H K O H K O H 2 K: 2 K: 1 H: 2 H: 1 O: 2 O: 1 2 2

  19. Balancing an Equation Determine how many of each atom are present. ___ H2 + ___ O2 ___ H2O H H O O H O H H: 2 H: 2 O: 2 O: 1

  20. Balancing an Equation The hydrogen is okay, but the oxygen is not. Add another H2O in order to balance the oxygen. ___ H2 + ___ O2 ___ H2O H H O O H O H H O H H: 2 H: 2 O: 2 O: 1

  21. Balancing an Equation The hydrogen is okay, but the oxygen is not. ___ H2 + ___ O2 ___ H2O H H O O H O H K O H 2 K: 2 K: 1 H: 2 H: 1 O: 2 O: 1 2 2

  22. Balancing an Equation ___ Al + ___ FeO  ___ Al2O3 + ___ Fe Al: 1 Al: 2 O: 1 O: 3 Fe: 1 Fe: 1

  23. Balancing an Equation Begin balancing the aluminum by adding a 2 _2_ Al + ___ FeO  ___ Al2O3 + ___ Fe Al: 1 Al: 2 O: 1 O: 3 Fe: 1 Fe: 1

  24. Balancing an Equation Recount the aluminum atoms _2_ Al + ___ FeO  ___ Al2O3 + ___ Fe Al: 2 Al: 2 O: 1 O: 3 Fe: 1 Fe: 1

  25. Balancing an Equation Move on to oxygen – Balance it by placing a 3 in front of FeO, and then recount the atoms _2_ Al + _3_ FeO  ___ Al2O3 + ___ Fe Al: 2 Al: 2 O: 3 O: 3 Fe: 3 Fe: 1

  26. Balancing an Equation By adding the 3, we also changed the iron – this is the only way to balance, so we now fix the iron by adding another coefficient _2_ Al + _3_ FeO  ___ Al2O3 + _3_ Fe Al: 2 Al: 2 O: 3 O: 3 Fe: 3 Fe: 3

  27. Balancing an Equation Now everything is balanced _2_ Al + _3_ FeO  ___ Al2O3 + _3_ Fe Al: 2 Al: 2 O: 3 O: 3 Fe: 3 Fe: 3

  28. Balancing an Equation Identify the number of each atom present – Start with atoms in the fewest compounds. We tend to keep H and O last. ___ SiO2 + ___ HF  ___ SiF4 + ___ H2O Si: 1 Si: 1 F: 1 F: 4 H: 1 H: 2 O: 2 O: 1

  29. Balancing an Equation Silicon is done, so move on to fluorine. ___ SiO2 + _4_ HF  ___ SiF4 + ___ H2O Si: 1 Si: 1 F: 4 F: 4 H: 4 H: 2 O: 2 O: 1

  30. Balancing an Equation Now move on to hydrogen. Since the compound has 2 hydrogen atoms in it, we multiply to get the correct number. ___ SiO2 + _4_ HF  ___ SiF4 + _2_ H2O Si: 1 Si: 1 F: 4 F: 4 H: 4 H: 4 O: 2 O: 2

  31. Balancing an Equation Oxygen is already done. Everything is balanced. ___ SiO2 + _4_ HF  ___ SiF4 + _2_ H2O Si: 1 Si: 1 F: 4 F: 4 H: 4 H: 4 O: 2 O: 2