unit 10: chemical equations
DESCRIPTION
Unit 10: Chemical Equations. Chapter Objectives. 1. To learn to write chemical equations 2. To correctly interpret chemical equations 3. To balance chemical equations. Chapter Objectives. 4. To classify chemical reactions 5. To predict products of chemical reactions - PowerPoint PPT PresentationTRANSCRIPT
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Unit 10:Chemical Equations
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Chapter Objectives
• 1. To learn to write chemical equations
• 2. To correctly interpret chemical equations
• 3. To balance chemical equations
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Chapter Objectives
• 4. To classify chemical reactions• 5. To predict products of
chemical reactions• 6. To write ionic and net ionic
equations
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Chemical Reactions
• In a chemical reaction, substances join together to form new substances
• The original substances present are called REACTANTS
• The new substances formed are called PRODUCTS
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Discussion of Chemical Reactions
• The general form of an equation is:• Reactants Products• The is read as “yields” or “reacts
to produce”
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Discussion of Chemical Reactions
• A + B C• Substance “A” and “B” react to
produce substance “C”
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Additional Symbols in Chemical Reactions
•+ used to separate reactants or products
•(s) means chemical is in solid state
•(l) means chemical is in liquid state
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Additional Symbols in Chemical Reactions
• (g) means chemical is in gas state• (aq) means chemical is dissolved
in water• *See Table 10-1 in book (page
278)
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Other Symbols
means something is added to the reaction–Usually this is heat
• Pt means a catalyst (Pt) is added
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Skeleton Equations
• Skeleton (Formula) Equation- the rough form of an equation
• It only shows the framework for the chemical reaction
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Write Skeleton Equations
• Sodium metal reacts with Oxygen gas to form solid Sodium Oxide
• Solid sulfur reacts with Fluorine gas to form gaseous Sulfur Hexafluoride when heated
• Nitrogen reacts with Hydrogen to form Ammonia (NH3) gas. Heat is required.
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Review-Write Skeleton Equations
• 1. Magnesium metal reacts with Chlorine to form solid Magnesium Chloride.
• 2. Aqueous Silver Nitrate reacts with aqueous Sodium Chloride to form solid Silver Chloride and aqueous sodium nitrate
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Law of Conservation of Mass
• The Law of Conservation of Mass states that mass is neither created or destroyed in a chemical reaction
• Because of this Law, it is necessary to balance chemical equations
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Balancing Chemical Equations
• In balanced chemical equations, each side of the equation has the same number of atoms of each element
•Coefficients are used to balance chemical equations
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Question• What is the difference between a
coefficient and subscript?• Coefficients are written before the
formulas• Subscripts are part of the formula•Never use SUBSCRIPTS to
balance an equation!!
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Rules for Balancing Equations
• 1. Determine the correct formulas for the reactants and products
• 2. Write the formulas for the reactants on the left side of the arrow. Write the formulas for the products on the right side of the arrow
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Rules Continued
• 3. Count the number of atoms of each element present on both sides of the equation
• 4. Balance the elements one at a time by placing coefficients in front of the formula.
• 5. Check to make sure each atom is balanced
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Additional Rules
• 6. Check to make sure that all coefficients are in the lowest possible ratio
• **If no coefficient is written, the coefficient is assumed to be “1”
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Examples
• Balance the following
• H2 (g) + O2 (g) H2O (l)
• Na (s) + Br2 (g) NaBr (aq)
• AgNO3 (aq) + Cu(s) Cu(NO3)2 (aq) + Ag(s)
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Classwork
•Complete Worksheet
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Review-balance the following
•1. Fe + O2 Fe2O3
•2. Al2O3 + H2 Al + H2O
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Quiz Review - Balance
•1. FeCl3 + NaOH Fe(OH)3 + NaCl
•2. CuCl2 + NaI CuI2 + NaCl
•3. H2O2 H2O + O2
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QUIZ
•1) C6H6 + O2 CO2 + H2O
•2) Mg + O2 MgO
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QUIZ REVIEW•1. Solid sulfur reacts with gaseous fluorine to produce aqueous sulfur hexafluoride
•2. Magnesium metal reacts with chlorine gas to make solid magnesium chloride
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Additional Questions
• Pb(NO3)2 + 2 NaOH Pb(OH)2 + 2 NaNO3
• How many oxygen atoms are on the reactant side?
• How many oxygen atoms are in 2 NaNO3?
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Balancing Equations -Determining Formulas
• To Balance Equations, you must remember how to write correct chemical formulas
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Example
• Write the balanced equation for solid aluminum reacting with oxygen gas to form solid aluminum oxide
• **Remember that the diatomic elements (Mr. BrINClHOF) appear with a subscript of two when alone
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Additional Examples
• 1. Carbon reacts with Chlorine to form Carbon Tetrachloride
• 2. Magnesium metal reacts with solid Zinc (II) Carbonate to form solid Magnesium Carbonate and Zinc metal
• 3. Nitrogen gas reacts with Hydrogen gas to form Ammonia (NH3) gas
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Types of Reactions
• There are five general types of reactions:
• Synthesis• Decomposition• Single Displacement• Double Displacement• Combustion
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Synthesis Reactions
• Synthesis reactions are also called combination reactions
• A synthesis reaction occurs when two substances combine to form a new compound
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Synthesis Reaction Continued
• The general form of a synthesis reaction is:
• A + X AX• Substance “AX” is the only
substance formed
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Examples of Synthesis Reactions
•2 Mg (s) + O2 (g) 2 MgO (s)
•Fe (s) + Cl2 (g) FeCl2 (s)
•U (s) + 3 F2 (g) UF6 (g)
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Decomposition Reaction
• In decomposition reactions, one substance breaks down (decomposes) into two or more simpler substances
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Decomposition Reactions Cont.
• General Form of Decomposition Reaction:
• AX A + X
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Examples of Decomposition Reactions
• 2 HgO (s) 2 Hg (l) + O2 (g)
• Ca(OH)2 CaO (s) + H2O (g)
• H2SO4 (aq) SO3 (g) + H2O (l)
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Write Correct Balance Equations
• 1. The synthesis of KCl• 2. The decomposition of
magnesium oxide• 3. The decomposition of hydrogen
peroxide (H2O2) into oxygen and water
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Write Correct Balance Chemical Equations for the following reactions
• 1. The synthesis of barium fluoride
• 2. The decomposition of Mg(OH)2
into magnesium oxide and water• 3. The decomposition of water
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Review-Write Balanced Equations
• 1. Gaseous hydrogen reacts with gaseous chlorine to form aqueous hydrogen chloride
• 2. Carbon monoxide gas reacts with gaseous oxygen to form solid carbon dioxide
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Write balanced equations
• 1. The synthesis of Iron (III) oxide• 2. The decomposition of cobalt
(IV) oxide• 3. The decomposition of calcium
hydroxide into calcium oxide and water
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Write Balanced Equations
•1) Na + Cl2
•2) HgCl2
•3) Fe(OH)3
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Single Replacement Reaction
• In a single replacement reaction (also called a displacement reaction), an element reacts with a compound
•A + BX AX + B
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Examples of Single Replacement Reactions
• Mg + Zn(NO3)2 Mg(NO3)2 + Zn
• Mg + 2 AgNO3 Mg(NO3)2 (aq) + 2 Ag
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Rules for Single Replacement Reactions
•Not all single replacement reactions occur
•You can determine if a reaction will occur by knowing the activity series of metals (See Handout)
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Rules for Single Replacement
• The activity series tell you if one metal can replace another metal in a reaction
• The Activity Series is ordered• Any metal that is above another
metal in the activity series WILL REPLACE the less reactive metal
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Activity Series• Li• K• Ca• Na• Mg• Al• Zn
• Fe• Pb• H*• Cu• Hg• Ag
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Predict if the following reactions will occur
• 1. Fe + H2O
• 2. Mg + LiNO3
• 3. Na + AgCl
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Write balanced equations for the following reactions
• 1. Mg + O2
• 2. FeCl3
• 3. Fe + ZnO • 4. Br2 + MgI2
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Review
• Predict the products and balance:
• 1) Mg + O2
• 2) HCl • 3) Na + H2SO4
• 4) Ag + ZnCl2
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Double Displacement Reactions
• In a double displacement reaction, two compounds react
• The compounds swap elements with each other
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Double Displacement Cont
• Compounds contain a positive and negative part
• In a double displacement, the positive parts swap places with each other as do the negative parts
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Examples
• PbCl2 (s) + Li2SO4 (aq) PbSO4 (s) + 2 LiCl (aq)
• ZnBr2 (aq) + 2 AgNO3 (aq) Zn(NO3)2 (aq) + 2 AgBr (s)
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Predict the Products of the following reactions and balance
• BaCl2 (aq) + KClO3 (aq)
• HCl (aq) + NaOH (aq) • RbBr (aq) + AgCl (aq)
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Combustion Reactions
• In a combustion reaction, a Hydrocarbon (compound containing Hydrogen and Carbon) reacts with Oxygen (O2)
• The products are CO2 and H2O
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Example
•2 C6H6 + 15 O212 CO2 + 6 H2O•*Combustion Reactions
commonly require large coefficients
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Guided Practice• Write the balanced equation
for the following combustion reactions:
• a. C4H8
• b. C6H12O6
• c. C7H16
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Independent Practice- Predict the products for the following reactions
• 1. Hf + N2 (Hf takes a +4 charge)
• 2. Mg + H2SO4
• 3. C2H6 + O2
• 4. Pb(NO3)2 + NaI
• 5. Fe + O2 (Fe takes a +3 charge)
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Ionic Equations
• Most ionic compound dissociate (or break apart) when dissolved in water to form its component ions
• For example: NaCl (aq) really looks like Na+(aq) and Cl- (aq)
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Soluble Vs. Precipitate
• Soluble means that the compound breaks down into its ions in water
• Ex) NaCl is soluble so it forms Na+ and Cl-
• Insoluble means that the compound doesn’t break down in water
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Precipitate Reactions
• In double replacement reactions, often one of the product will be insoluble
• The insoluble product is referred to as a precipitate
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Practice• Determine if soluble or insoluble:
• A) NaCl B) K2O
• C) Fe(NO3)3 D) AgCl
• E) BaS F) Cd(OH)2
• G) FeCl3 H) PbCO3
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Ionic Equations Continued• To write a Complete Ionic
Equation:• Write the aqueous substances as
ions (leave any substances in gas, liquids, & solids alone)
• Example:
• AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)
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Writing Ionic Equations • 1. (NH4)2S (aq) + Cd(NO3)2
(aq) NH4NO3 (???) + CdS (???)
• 2. Zn(NO3)2 (aq) + (NH4)2S (aq) ZnS (???) + NH4NO3 (???)
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Spectator Ions
• Spectator Ions-Ions that are not directly involved in a reaction
• Spectator ions show up on both sides of the equation
• Spectator Ions cancel out
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NET Ionic Equations
• Net Ionic Equation-Indicate the particles that actually take part in a reaction
• The Net Ionic Equation does NOT include spectator ions
• Net Ionic Equations must be balanced according to atoms and charge
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Write Net Ionic Equations
• 1. (NH4)2S (aq) + Cd(NO3)2 (aq)
• 2. Zn(NO3)2 (aq) + (NH4)2S (aq)