: Types of Chemical Reactions

Transcription

1 : Types of Chemical Reactions

2 Chemical Reactions There are millions of known chemical reactions! We can group these reactions by their reaction patterns, making it easier to predict products of reactions. When predicting products for any reaction, follow these steps: Step 1: Identify reactant(s) (write formula with state!) Step 2: Identify reaction type Step 3: Predict the product(s) (formula and state) using the rules for the specific reaction type Step 4: Balance the equation

3 To predict states: Chemical Reactions An ELEMENT on its own use the state on periodic table A COMPOUND: IONIC will always be solid MOLECULAR are usually gases Exception: H 2 O is liquid ACIDS and BASES are aqueous Any SOLUTION is aqueous Other important rules to remember: Whenever a NEW ionic compound is formed, use the ionic charges to determine the formula! Diatomic Molecules! ie: the element chlorine is not Cl, it is always Cl 2!

4 1. Synthesis Reactions Definition: When two reactants combine to form one larger or more complex product Pattern: A + B AB a) Synthesis of Ionic Compounds (Metal and Non-Metal) Use ionic charges of the reactants to predict the product Example: The reaction of magnesium with oxygen

5 1. Synthesis Reactions b) Synthesis of Molecular Compounds (Non-Metals) i) Reactions involving Hydrogen Although hydrogen is in Group 1, it is a non-metal and usually forms molecular compounds. But, we still use ionic charges to predict the products. Example: Synthesis of hydrogen chloride

6 1. Synthesis Reactions ii) Reactions not involving Hydrogen Difficult to predict the products. They often depend on the reaction conditions. Only way to identify the products is by chemical tests. For our purposes, simply combine the two nonmetals into the compound specified Example: Synthesis of phosphorus tribromide

7 1. Synthesis Reactions c) Synthesis Reactions involving oxides i) Acidic oxides Non-metals react with oxygen to form non-metallic oxides Ex: The synthesis of carbon dioxide Then, when dissolved in water, non-metallic oxides produce acidic solutions (the oxyacid that corresponds to the original nonmetal is formed) Ex: carbon dioxide reacts with water

8 1. Synthesis Reactions ii) Basic oxides Metals react with oxygen to form metallic oxides Example: Sodium and oxygen Then, when dissolved in water, metallic oxides produce basic solutions (The metal combines with hydroxide) Example: Sodium oxide reacts with water

9 1. Synthesis Reactions Practice! a) Show the synthesis of calcium oxide. Then, show the reaction when it reacts with water. b) Show the 2 step synthesis of sulfuric acid. (Formed when sulfur trioxide reacts with water).

10 2. Decomposition Reactions Definition: A large or more complex compound breaks down into two (or more) simpler products. Usually requires heat or energy (Δ) Δ Pattern: AB A + B a) Simple Ionic or Molecular Compounds The compound breaks down into its elements Example: Decomposition of potassium chloride Example: Decomposition of ammonia

11 2. Decomposition Reactions b) Complex Compounds A compound breaks down into two simpler compounds Often difficult to predict, except: Carbonates decompose into a metal oxide and CO 2 Example: The decomposition of calcium carbonate Example: The decomposition of lithium carbonate

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13 3. Single Displacement Reactions Definition: When one element displaces/replaces another element in a compound. Pattern: A + BC AC + B if A is a metal A + BC BA + C If A is a non-metal Example: Zinc reacts with copper (II) sulfate solution Example: Bromine reacts with magnesium oxide solution

14 3. Single Displacement Reactions The Activity Series of Metals Not all single displacement reactions on paper actually occur. It depends on the reactivity of the two metals. The Activity Series is a list of metals and their reactivity. (see handout) The most reactive metals are on top An element (on its own) can only displace another element (in a compound) if it is MORE REACTIVE (higher on the activity series) Otherwise, no reaction occurs! The farther apart two elements are, the quicker the reaction

15 3. Single Displacement Reactions

16 3. Single Displacement Reactions a) Reactions Involving a Metal and an Ionic Compound Use the activity series to determine if a reaction occurs If reaction occurs, write the products If no reaction occurs, just write NO REACTION. Example: Magnesium metal is placed in a solution of copper (II) sulfate Example: Lead is placed in a zinc nitrate solution

17 3. Single Displacement Reactions b) Reactions Involving a Metal and Water or Acid (H+) Same idea as above: Hydrogen is also on the activity series **Treat acids and water as if they are ionic compounds (with an H+) H 2 O = H + OH - H 2 SO 4 = H + H + SO 4 2- Example: Lithium is added to sulfuric acid Example: Sodium is added to water

18 3. Single Displacement Reactions c) Reactions Involving a Non-Metal Halogens have their own activity series follows group pattern Example: The reaction of chlorine and potassium iodide solution

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20 4. Double Displacement Reactions Definition: When elements in two compounds displace each other/trade places, producing two new compounds. Pattern: AB + CD AD + CB ** Like replaces like (metals switch places)

21 4. Double Displacement Reactions Recall: Solubility Solution - HOMOGENEOUS mixture of 2 or more substances (ie: salt water) Solute the substance that dissolves IN a solvent (salt) Solvent the substance that dissolves the solute (water) Solubility the quantity of solute that dissolves in a given quantity of solvent at a given temperature (aq) aqueous is soluble in solution (s) - solid precipitate is NOT soluble in solution

22 4. Double Displacement Reactions a) Precipitation Reactions (Two ionic compounds) Reactions between two compounds don t ALWAYS happen. It depends on their solubility. If a precipitate forms, a reaction occurs, because one of the new compounds is not soluble in the solution of the other compound. If no precipitate forms, there is no reaction How do we determine if a precipitate forms? USE the SOLUBILITY chart (see handout) Practice: Determine if the following compounds are soluble (aq) or insoluble (s) in water: a) AgCl b) MgCl 2 c) Na 2 CO 3 d) BaSO

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24 4. Double Displacement Reactions Example: Solutions of potassium chloride and silver nitrate are combined. Example: Solutions of potassium sulfate and iron (III) chloride are combined.

25 4. Double Displacement Reactions b) Reactions that Produce a Gas Double displacement reactions involving an acid can produce gases. Gases may be produced in two ways: 1. Directly Example a metal sulfide will produce hydrogen sulfide gas 2. Indirectly an unstable product can decompose into water and a gas Example: A carbonate Gases formed: Sulfides H 2 S Carbonates CO 2 Sulfites SO 2 Example: A sulfite

26 4. Double Displacement Reactions c) Neutralization Reactions i) With a hydroxide compound Pattern: Acid + base Salt + water Acid has H+, Base has OH - form HOH (H 2 O) - these ions combine to Other cation and anion combine to form a SALT (ionic compound) Example: hydrochloric acid and sodium hydroxide

27 4. Double Displacement Reactions c) Neutralization Reactions ii) With a carbonate compound Pattern: Acid + carbonate ionic compound + water + carbon dioxide Example: Calcium carbonate reacts with sulfuric acid to produce carbonic acid: But, carbonic acid immediately decomposes into water and carbon dioxide The chemical equation for the net reaction of calcium carbonate and sulfuric acid is:

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29 5. Combustion Reactions a) Complete Combustion Definition: A chemical reaction in which fuel burns in oxygen Common fuels are hydrocarbons with the general formula C x H y. Methane is CH 4, propane is C 3 H 8 Releases energy in the form of heat and light

30 5. Combustion Reactions a) Complete Combustion Formula: C X H y + O 2 (g) H 2 O (g) + CO 2 (g) Occurs when there is plenty of oxygen Products are energy, water vapour, and carbon dioxide The ideal way to burn a fuel it produces the cleanest (least sooty) and hottest flames The blue flame on a gas stove is an example of complete combustion Example: Burning of natural gas, CH 4

31 5. Combustion Reactions b) Incomplete Combustion Formula: C X H y + O 2 (g) H 2 O (g) + CO 2 (g) + CO (g) + C (s) Occurs when the oxygen supply is limited Products are energy, water vapour, carbon dioxide, carbon monoxide, and carbon (soot) Flames are often sooty, yellow, and cooler The burning of a log in a fireplace is an example of incomplete combustion There are many environmental concerns related to incomplete combustion Example: Incomplete combustion of heptane (C 8 H 18 ), a hydrocarbon in gasoline

32 5. Combustion Reactions Practice: Compare the complete and incomplete combustion of propane, C 3 H 8.

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