Chemical Reactions 9.2: Classifying Chemical Reactions.
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Transcript of Chemical Reactions 9.2: Classifying Chemical Reactions.
Chemical Reactions
9.2: Classifying Chemical Reactions
Objectives
• Classify chemical reactions.• Identify the characteristics of
different classes of chemical reactions.
Other symbols to know:• A double arrow indicates that a reaction is
reversible.• A downwards-pointing arrow may be written after
a formula. It indicates that the substance is a precipitate (a solid).
• An upwards-pointing arrow may be written after a formula. It indicates that the substance is a gas.
• Pt A chemical formula written above an arrow in an equation indicates that that substance is a catalyst. A catalyst is a substance that will increase the rate of a reaction but not be consumed in the reaction.
• Recall that a triangle ( ) above the arrow indicates that heat must be added for the reaction to occur.
Classifying Chemical Reactions
• Chemists classify chemical reactions in order to organize the many reactions that occur daily in our world.
• Recognizing the patterns in chemical reaction allows for the prediction of products that will form.
Classifying Chemical Reactions
1. Synthesis reactions
A + B AB
• 2 or more substances (elements or compounds) react to produce a single product.
Classifying Chemical Reactions
• Synthesis reactions• A + B AB
• 8 Fe + S8 8 FeS
• CaO + H2O Ca(OH)2
• 2SO2 + O2 2SO3
Practice Problems
1 - Aluminum and sulfur react to form …
2 - Water and dinitrogen pentoxide react to produce nitric acid.
3 – Magnesium + oxygen ?
Classifying Chemical Reactions
2. Combustion Reactions• Any reaction in which oxygen
combines with a substance and releases energy in the form of heat and light.
Combustion Reactions
• C + O2 CO2
• 2H2 + O2 2H2O
• 2SO2 + O2 2SO3
• Can be classified as a synthesis reactions
• Can also be classified as combustion reactions
Combustion of Hydrocarbons
• All hydrocarbons burn in oxygen. If the combustion is complete, the reaction will always yield carbon dioxide and water.
• C10H8 + 12 O2 10 CO2 + 4 H2O
Practice Problems
1 - Nitrogen dioxide and oxygen react to produce dinitrogen pentoxide.
2 - Ethane (C2H6) burns completely in the air.
3 – Iron forms rust (Fe2O3) when exposed to air.
Classifying Chemical Reactions
3. Decomposition Reactions
• AB A + B
• One reactant breaks down into 2 or more products.• the “opposite of synthesis”• often REQUIRE energy to occur
Classifying Chemical Reactions
• Decomposition Reaction• AB A + B
• 2 H2O 2 H2 + O2
• NH4NO3 N2O + 2H2O
Practice Problems1 - Aluminum oxide decomposes when
electricity is passed through it.2 - Heating sodium hydrogen carbonate
produces sodium carbonate, carbon dioxide, and water.
3 - Nickel (II) hydroxide decomposes to produce nickel (II) oxide and water.
Classifying Chemical Reactions
4. Single Replacement
• A + BX AX + B or• X + BY BX + Y
• Atoms of one element replace the atoms of another element that is in a compound (Look for an element reacting with a compound)
Classifying Chemical Reactions
• Single Replacement• A + BX AX + B
• There are 2 kinds following this general pattern:
1 - Mg + 2 H2O Mg(OH)2 + H2
(a metal ion replaces a H+)2 - Cu + 2AgNO3 2Ag + Cu(NO3)2
(a metal ion replaces another metal ion)
A metal ion will not always replace a H ion or another metal ion. It will only replace the H or metal ion IF it has a higher reactivity than those elements.
A Reactivity SeriesReactivity is defined as the ability to react with another substance. A reactivity series ranks metals by reactivity. (See pg. 293 in textbook, Fig. 13.)
Hydrogen
Will these reactions occur?
• Ag + Cu(NO3)2 ?
• Ca + LiBr ?
• Zn + PbCl2 ?
• Al + MgSO4 ?
Classifying Chemical Reactions• Single replacement reactions can follow
another pattern: X + BY BX + Y
F2 + 2NaBr 2NaF + Br2
(a halogen replaces another halogen)
*Reactivity of Halogens decreases from top to bottom.
(Fluorine will replace bromine but bromine will not replace fluorine!)
Practice Problems
• K + ZnCl2 ?
• Fe + CuSO4 ?
• Br2 + MgCl2 ?
• F2 + HCl ?
• Fe + Na3PO4 ?
• Mg + AlCl3 ?
Classifying Chemical Reactions
5. Double Replacement Reaction
• AX + BY AY + BX
• Ions are exchanged between 2 compounds.
Classifying Chemical Reactions
5. Double Replacement Reaction
• AX + BY AY + BX
To correctly predict the products of these reactions, pair up “the outsides” and “the insides.” Don’t forget to “criss-cross” the charges between each pair, in order to write the correct formula.
Classifying Chemical Reactions
• All double replacement reactions will produce either water, a precipitate, or a gas.• Pb(NO3)2 + 2 KI PbI2 (s) + 2 KNO3
(A precipitate is a product.)
• Ca(OH)2 + 2HCl CaCl2 + 2H2O
(Water is a product.)• KCN + HBr KBr + HCN (g)
(A gas is produced.)
Classifying Chemical Reactions
• Another important point to note is that the components of double-replacement reactions are usually always dissolved in water.
Practice Problems• Predict the products:
• Al(NO3)3 + H2SO4
• NaOH + CuCl2
• Write the equations.• Lithium iodide and silver nitrate react to
produce solid silver iodide and lithium nitrate.
• Sodium hydroxide and phosphoric acid react to produce water and sodium phosphate.