Chemical Reactions and Equations Chapter 9 - PowerPoint PPT Presentation

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Title: Chemical Reactions and Equations Chapter 9


1
Chemical Reactionsand EquationsChapter 9
2
Write the chemical reaction
  • Write the formula equation for the following
  • Ammonia reacts with hydrochloric acid to form
    ammonium chloride.

3
Learning Objectives
  • Be able to balance chemical equations by applying
    the law of conservation of mass.
  • Be able to recognize direct combination
    (synthesis), decomposition, single displacement,
    double displacement, combustion and
    neutralization reactions.

4
Law of Conservation of Matter
  • Conservation of Matter in all chemical and
    physical changes, matter is neither created or
    destroyed
  • The total mass in a chemical reaction remains
    constant
  • Antoine Lavoisier
  • Made accurate and precise measurements during
    chemical reactions

5
Chemical Reactions
  • A chemical change is really a chemical reaction
  • Has 2 parts
  • Reactants the substances you start with
  • Products the substances you end up with
  • The reactants turn into the products
  • 4 Fe 3 O2 ? 2 Fe2O3
  • Reactants ? products

6
In a chemical reaction
  • Atoms are rearranged into new molecules
  • Can be described several ways
  • 1. In a sentence
  • Copper reacts with chlorine to form copper (II)
    chloride.
  • 2. In a word equation
  • Copper chlorine copper (II) chloride
  • 3. In chemical formulas
  • Cu Cl2 ? CuCl2

7
Symbols in equations-
  • the arrow ? separates the reactants from the
    products
  • (s) after the formula solid
  • (g) after the formula gas
  • (l) after the formula liquid
  • (aq) after the formula - aqueous solution,
    dissolved in water.

8
Symbols used in equations
  • Double arrow indicates a reversible
    reaction
  • shows that
    heat is supplied to the reaction
  • is used to indicate a catalyst
    is supplied, in this case, platinum.

9
What is a catalyst?
  • A substance that speeds up a reaction, without
    being changed or used up by the reaction.
  • Enzymes are biological or protein catalysts.

10
Balanced Equation
  • Atoms cant be created or destroyed
  • All the atoms at the beginning must appear in the
    end
  • A balanced equation has the same number of atoms
    of each element on both sides of the equation

11

O

C
C
O
O
O
  • C O2 CO2
  • This equation is already balanced
  • What do we do when an equation is not balanced?

12

O

C
C
O
O
  • C O2 CO
  • We need one more oxygen in the products.
  • Cant change the formula, because it describes
    what the substance is (carbon monoxide in this
    example)

13
C
O

O

C
O
C
O
  • Must be used to make another CO
  • But where did the other C come from?

14
C
C
O

O

O
C
O
C
  • Must have started with two C
  • 2 C O2 2 CO

15
Rules for balancing
  • Assemble, write the correct formulae for all the
    reactants and products
  • Count the number of atoms of each type appearing
    on both sides
  • Balance the elements one at a time by adding
    coefficients (the numbers in front) - save H and
    O until last!
  • Check to make sure it is balanced.

16
Never
  • Never change a subscript to balance an equation.
  • If you change the formula you are describing a
    different reaction.
  • H2O is a different compound than H2O2
  • Never put a coefficient in the middle of a
    formula
  • 2 NaCl is okay, Na2Cl is not.

17
Balancing Equations Examples
  • H2 (g) O2 (g) ? H2O (l)
  • Zn HCl ? H2 ZnCl2
  • Pb (NO3)2 K2S ? PbS KNO3

18
Try a couple
  • Write the balanced chemical equation for
    dinitrogen pentoxide reacts with water to produce
    nitric acid.

N2O5 H2O ? HNO3
19
Try a couple
  • Write the balanced chemical equation for
    magnesium reacts with titanium (IV) chloride to
    produce magnesium chloride and titanium.

Mg TiCl4 ? MgCl2 Ti
20
Balance the following
  • iron(II) chloride sodium phosphate ? sodium
    chloride iron (II) phosphate
  • FeCl2 Na3PO4 ? NaCl Fe3(PO4)2

21
Balance the following- Combustion Reaction (CO2
and H2O are the products)
  • Write a balanced chemical equation for the
    reaction in which benzene (C6H6) reacts with
    oxygen gas to produce carbon dioxide and water.
  • C6H6 O2 ? CO2 H2O

22
Five General Types of Chemical Reactions
  • Direct Combination (Synthesis)
  • Decomposition
  • Single-Replacement
  • Double-Replacement
  • Combustion
  • By knowing the type of reaction that is
    occurring, you can predict the products that will
    be formed.

23
I. Direct Combination Reactions (also called
synthesis reactions).
  • General form A B ? AB
  • (two reactants make a single product)
  • A, B elements or compounds
  • AB compound consisting of A and B
  • This is the only type of chemical reaction in
    which there is a single product formed. This
    single product is always more complex than the
    reactants.

24
Examples of Synthesis Reactions
  • calcium oxygen yields calcium oxide 2Ca O2
    ? 2CaO
  • carbon dioxide water yields carbonic acid
  • CO2 H2O ? H2CO3
  • Notice All equations show two (or more)
    reactants, but only one product.
  • http//www.ric.edu/ptiskus/reactions/Index.htm

25
II. Decomposition Reactions
  • General form AB ? A B
  • (one reactant makes two or more products)
  • AB compound
  • A, B elements or simpler compounds
  • This is the only type of chemical reaction in
    which there is a single reactant. This single
    reactant is always more complex than the
    products.

26
Decomposition Reactions Examples
  • water yields hydrogen and oxygen
  • 2H2O ? 2H2 O2
  • marble (calcium carbonate) yields calcium oxide
    and carbon dioxide
  • CaCO3 ? CaO CO2
  • Notice all equations show a single reactant
    decomposing into two (or more) products.
  • http//www.ric.edu/ptiskus/reactions/Index.htm

27
III. Single-Replacement Reactions
  • General Form A BX ? AX B
  • One element and one compound recombine (switch
    partners)
  • AX, BX ionic compounds
  • A, B elements
  • X ion that switches partners
  • This is the only type of chemical reaction where
    a compound reacts with an element to make another
    compound and element.

28
Single-Replacement Examples
  • magnesium metal and copper (II) sulfate
  • Mg CuSO4 ? MgSO4 Cu
  • iron metal and copper (II) sulfate)
  • Fe CuSO4 ? FeSO4 Cu
  • Notice In both reactions, an element combines
    with a compound to create a new compound and a
    different element
  • www.ric.edu/ptiskus/reactions/Index.htm

29
IV. Double-Replacement Reactions
  • General form AX BY ? AY BX
  • (Positive ions in two compounds are exchanged)
  • A,B positive ions
  • X,Y negative ions
  • This is the only type of chemical reaction with
    two compounds as reactants and two compounds as
    products.

30
Double Replacement Examples
  • calcium carbonate and hydrochloric acid yield
    calcium chloride and carbonic acid
  • CaCO3 2HCl ? CaCl2 H2CO3
  • Notice in this reaction, two ionic compounds
    exchange ions to form two new ionic compounds
  • www.ric.edu/ptiskus/reactions/Index.htm

31
Rules of Double-Displacement Reactions
  • Reactants must be dissolved in water (releasing
    the ions).
  • Will occur if one of the products
  • is a molecule (covalent),
  • a precipitate (solid comes out of solution), or
  • an insoluble gas.

32
V. Combustion Reactions
  • General Form
  • CxHy O2 ? H2O CO2
  • (hydrocarbon and oxygen react to form carbon
    dioxide and water)
  • This is the only type of chemical reaction where
    something reacts with oxygen and forms carbon
    dioxide and water

33
Combustion Examples
  • Methane reacts with oxygen
  • CH4 (methane) 2O2 ? 2H2O CO2
  • Gasohol reacts with oxygen
  • C2H5OH (gasohol) 3O2 ? 3H2O 2CO2
  • Notice in both cases, water and carbon dioxide
    are the products.
  • www.ric.edu/ptiskus/reactions/Index.htm

34
Convert these to equations
  • Solid iron (III) sulfide reacts with gaseous
    hydrogen chloride to form iron (III) chloride and
    hydrogen sulfide gas.
  • Nitric acid dissolved in water reacts with solid
    sodium carbonate to form liquid water and carbon
    dioxide gas and sodium nitrate dissolved in
    water.
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