Chemical Reactions

 In chemical reactions, one or more substances change into different substances.  For example: combustion

Word Equations and Chemical Equations  Chemists use equations to describe chemical reactions.  Word equations show the names of the materials in the chemical reaction.  Chemical equations show the chemical formulas of the materials in the chemical reaction. REACTANTS PRODUCTS (starting materials)(yields)(ending materials)

 Word equation: sodium + chlorine sodium chloride  Chemical equation: Na + Cl NaCl sodium chlorinechemical reaction sodium chloride

 energy + copper(II) carbonate carbon dioxide + copper(II) oxide  energy + CuCO 3 CO 2 + CuO

Common State Symbols in Chemical Equations State SymbolMeaningExample (s)Solidsodium chloride NaCl (s) (l)Liquidwater H 2 O (l) (g)Gaseoushydrogen H 2(g) (aq)Aqueous (dissolved in water) aqueous sodium chloride solution NaCl (aq)

 zinc + copper (II) sulphatezinc sulphate + copper + energy  Zn (s) + CuSO 4(aq) ZnSO 4(aq) + Cu (s) + energy

Write the word equation:  Acetic acid (vinegar) and sodium hydrogen carbonate (baking soda) react to form water, carbon dioxide and sodium acetate.  Aluminum metal reacts with oxygen from the air to form a protective coating called aluminum oxide.  Water and carbon dioxide are produced when propane burns in oxygen.  Bread rises due to the action of a single-celled organism called yeast. Yeast converts some glucose molecules in bread dough into carbon dioxide and ethanol. Carbon dioxide and ethanol bubble through the dough, making it rise.

Consider the following reaction:  AgNO 3(aq) + NaCl (aq) AgCl (s) + NaNO 3(aq)  1. Name the reactants and products in this reaction.  2. Name the chemicals that are dissolved in water.  3. Name the white solid.  4 What physical properties do both reactants have in common?

The Law of Conservation of Mass  Chemist Antoine Lavoisier’s work in the 1700s resulted in the Law of Conservation of Mass. It states that: In a chemical reaction, the total mass of the products is always the same as the total mass of the reactants.

 For example: The electrolysis of water  H 2 O  H 2 + O 2 is NOT a balanced chemical equation.  Why? Because the number of H and O atoms in the reactants does not equal the number of H and O atoms in the products.  How can we make a balanced chemical equation?

Balancing Chemical Equations  The electrolysis of water yields oxygen gas and hydrogen gas.  a) Write the word equation. water  oxygen + hydrogen  b) Write the skeleton equation. H 2 O (l)  O 2(g) + H 2(g)  c) Write the balanced chemical equation. 2H 2 O (l)  O 2(g) + 2H 2(g)

 Iron reacts with oxygen to produce Iron (III) oxide (Fe 2 O 3 )  a) Write the word equation. iron + oxygen  iron (III) oxide  b) Write the skeleton equation. Fe + O 2  Fe 2 O 3  c) Write the balanced chemical equation. 4Fe + 3O 2  2Fe 2 O 3

Practice  For the following reactions, write:  the word equation  the skeleton equation (unbalanced chemical equation)  the balanced equation 1. Potassium hydroxide and hydrogen are produced when potassium is placed in water. 2K + 2H 2 O  2KOH + H 2 2. The iron reacts with oxygen to produce rust, which is iron (III) oxide. 4Fe + 3O 2  2Fe 2 O 3

3. Zinc reacts with lead (IV) nitrate to produce zinc nitrate and lead. 2Zn + Pb(NO 3 ) 4  2Zn(NO 3 ) 2 + Pb 4. Calcium chloride reacts with silver nitrate to produce a white precipitate, silver chloride, and calcium nitrate. CaCl 2 + 2AgNO 3  2AgCl + Ca(NO 3 ) 2 5. Calcium carbonate decomposes into calcium oxide and carbon dioxide. CaCO 3  CaO + CO 2

6. Carbon monoxide and hydrogen gases are produced when carbon is placed in water. C + H 2 O  CO + H 2 7. In a hydrogen bomb, hydrogen gas and oxygen reacted to make water. 2H 2 + O 2  2H 2 O 8. Nitrogen monoxide from automobile exhaust reacts with oxygen to produce nitrogen dioxide, which is a toxic brown gas. 2NO + O 2  2NO 2

9. Hydrogen sulphide can be broken into hydrogen gas and sulphur. H 2 S  H 2 + S 10. Calcium metal and water combine to produce calcium hydroxide and hydrogen gas. Ca + 2H 2 O  Ca(OH) 2 + H 2