“Chemical Reactions”

All chemical reactions…  have two parts: 1.Reactants = the stuff you start with 2.Products = the stuff you end up with  The reactants will turn into the products.  Reactants  Products

Reactants Products

Label Reactants and Products Ca(OH) 2 + 2HF  2H 2 O + CaF 2

Label Reactants and Products Ca(OH) 2 + 2HF  2H 2 O + CaF 2 reactants products

In a chemical reaction  Atoms aren’t created or destroyed (based on the Law of Conservation of Mass)  A reaction can be described several ways: #1. In a sentence every item is a word Copper reacts with chlorine to form copper (II) chloride. #2. In a word equation some symbols used Copper + chlorine  copper (II) chloride

 #3. In a skeleton equation : use all symbols but are not balanced.  #4. In a balanced chemical equation no words are used; only symbols. Cu (s) + Cl 2 (g)  CuCl 2  s) Cu (s) + Cl 2 (g)  CuCl 2  s)

Symbols in equations?  the arrow (→) separates the reactants from the products (arrow points to products)  Read as: “reacts,” “forms” or “yields”  The plus sign is read as “and,” “is added to,” or “reacts with”  (s) after the formula = solid: Fe (s)  (g) after the formula = gas: CO 2(g)  (l) after the formula = liquid: H 2 O (l)

Symbols used in equations  (aq) after the formula = an aqueous solution:  NaCl (aq) is a salt water solution (salt dissolved in water)   used after a product = a gas has been produced: H 2 ↑   used after a product = solid has been produced: PbI 2 ↓

Symbols used in equations ■ double arrow = a reversible reaction (more later) ■ = heat is supplied to the reaction ■ = a catalyst is used (in this case, platinum is the catalyst)

What is a catalyst?  A substance that speeds up a reaction, without being changed or used up by the reaction.

The Skeleton Equation The Skeleton Equation  Uses formulas and symbols to describe a reaction  Does not indicate how many; this means the equation is NOT balanced  All chemical equations are a description of the reaction.

Write a skeleton equation for: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (III) chloride and hydrogen sulfide gas. Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (III) chloride and hydrogen sulfide gas. Fe 2 S 3 (s) + HCl (g)  FeCl 3(s) + H 2 S (g) Fe 2 S 3 (s) + HCl (g)  FeCl 3(s) + H 2 S (g) Fe +3 S -2 H +1 Cl -1 Fe +3 Cl -1 H +1 S -2

Write a skeleton equation for: Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water. Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water. HNO 3(aq) + Na 2 CO 3(s)  H 2 O (l) + CO 2(g) NaNO 3(aq) H +1 NO 3 -1 Na +1 CO 3 -2 H2OH2O CO 2 Na +1 NO 3 -1

Now, write a sentence for these equations: 1. Fe (s) + O 2(g)  Fe 2 O 3(s) 1. Fe (s) + O 2(g)  Fe 2 O 3(s) Solid iron reacts with oxygen gas to form solid iron (III) oxide. 2. NO 2(g)  N 2(g) + O 2(g) 2. NO 2(g)  N 2(g) + O 2(g) Nitrogen dioxide gas breaks down to form nitrogen gas and oxygen gas. Nitrogen dioxide gas breaks down to form nitrogen gas and oxygen gas.

1. sodium chloride + lead (II) nitrate  lead (II) chloride + sodium nitrate

2. iron + chlorine  iron (III) chloride

3. barium + water  barium hydroxide + hydrogen gas

4. When chlorine gas reacts with carbon tetrahydride, carbon tetrachloride and hydrogen chloride are produced.

5. When sodium oxide is added to water, sodium hydroxide is produced.

6. In a blast furnace, iron (III) oxide and carbon monoxide gas react to form carbon dioxide gas and iron.

7. Iodine crystals react with chlorine gas to produce iodine trichloride.