ch. 8 - chemical equations and reactionsweb[1]

8/8/2019 Ch. 8 - Chemical Equations and ReactionsWeb[1]

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Chapter 8

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` Chemical Reaction: process by which one or more

substances are changed into one or more different

substances.

` Original Substances Resulting

Substances

` Reactants Products

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Chemical equations show the conversion ofreactantsreactants (the molecules shown on the left of thearrow) into productsproducts (the molecules shown on theright of the arrow).x

A + sign separates molecules on the same sidex The arrow is read as yields

x Example

C + O2 CO2x This reads carbon plus oxygen react to yield carbon

dioxide

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x Solid (s)

x Liquid (l)

x Gas (g)

xAqueous solution (aq)

x CatalystH2SO4

x Escaping gas (o)

x Change of temperature (()

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` Easily observed changes that indicate a

chemical reaction has occurred

1. Evolution of heat and light

2. Production of a gas3. Formation of a precipitate

4. Color Change

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` Write a word equation to describe the reaction of

methane (natural gas) as it burns in the air to

produce carbon dioxide and water vapor.` Methane + oxygen carbon dioxide + water

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` Chemical Equation: represents with symbols and

formulas, the identities and relative amounts of the

reactants and products in a chemical reaction.

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` Law of Conservation of Mass must be taken intoaccount.

`Adjust equation so that the same type of atoms

and numbers of atoms are the same on bothsides of the equation.

` CH4(g) + O2(g) CO2(g) + H2O(g)

` CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

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` Solid sodium oxide is added to water (at room

temp.) and forms sodium hydroxide which is

dissolved in water.` Sodium oxide(s) + water(l) sodium

hydroxide (aq)` Na2O(s) + H2O(l) NaOH(aq)` Na2O(s) + H2O(l) 2NaOH(aq)

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` Hydrogen peroxide in an aqueous solution

decomposes to produce oxygen and water.

` Hydrogen peroxide oxygen + water

` H2O2(aq) O2(g) + H2O(l)` 2H2O2(aq) O2(g) + 2H2O(l)

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1. Write the chemical equation with the correctformulas for the reactants and products.

2. Count the number and types of atoms on bothsides of the equation.

3. Balance the atoms of the elements that appearonly once on each side of the equation.

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4. Balance polyatomic ions that appear on each

side of the equation.

5. Balance hydrogen and oxygen after all other

atoms have been balanced.6. Check both sides count each element.

7. Use lowest coefficients.

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` Bromine

` Iodine

` Nitrogen

` Chlorine` Hydrogen

` Oxygen

` Fluorine

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BrINClHOF

H7

HON Family


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` Zinc(s) + hydrochloric acid(aq) zinc chloride (aq) and

hydrogen gas.

` Zn(s) + HCl (aq) ZnCl2(aq) + H2(g)

` Zn(s) + 2 HCl(aq) ZnCl2(aq) + H2(g)

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` Combustion Reaction contains a hydrocarbon +

oxygen to yield carbon dioxide and water.

` Balance carbon first, then hydrogen and finally

oxygen.` C2H6 + O2 CO2 + H2O

` 2C2H6 +7 O2 4 CO2 + 6H2O

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Five Basic Types of Chemical Reactions:

1. Synthesis

2. Decomposition

3. Single-replacement4. Double-replacement

5. Combustion

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` Two or more substances combine to form a new

compound.

` A + X AX

(A & X may be compounds or elements)

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` Mg(s) + O2(g) MgO(s)2Mg(s) + O2(g) 2MgO(s)

` Ba(s)

+ S8 (s)

BaS(s)

8Ba (s) + S8 (s) 8 BaS(s)` Na(s) + Cl2(g) NaCl

` 2 Na(s) + Cl2 (g) 2NaCl

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` A single compound undergoes a reaction that

produces 2 or more simpler substances.

` AX A + X(A & X can be elements or compounds)

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` H20 (l) H2 (g) + O2 (g)` 2H20 (l) 2H2 (g) + O2 (g)

`

HgO (s)

Hg (g) + O2 (g)` 2HgO (s) 2Hg (g) + O2 (g)

` CaCO3 (s) CaO (s) + CO2 (g)

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` One element replaces a similarelement in a

compound.

` A + BX AX + Bor

` A + BX BA + X

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2Al(s) + 3Pb(NO3)2 (aq) 3Pb(s) + 2Al(NO3)3 (aq)

`Al replaces Pb

` Cl2(g) + 2 KBr(aq) 2KCl(aq) + Br2(g)

` Cl replaces Br

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` The ions of two compounds exchange places in

an aqueous solution to form two new compounds.

` AX + BY AY + BX

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2KI(aq) + Pb(NO3)2(aq) 2 KNO3(aq) + PbI2 (s)

` K cation replaces Pb cation

` I anion replaces nitrate anion

FeS(s) + 2HCl(aq) H2S(g) + FeCl2(aq)

`

Fe cation replaces H cation` S anion replaces Cl anion

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` A substance combines with oxygen releasing a

large amount of energy in the form of heat and

light.

` Hydrocarbon + O2 CO2 + H2O

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` CH4 (g) + O2 (g) CO2 (g) + H2O (g)

` CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (g)

` C3H8 (g) + O2 (g) CO2 (g) + H2O (g)

` C3H8 (g) + 5 O2 (g) 3CO2 (g) + 4H2O (g)

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` Read 8-2, pages 256-264

` Section Review, p. 264: 1-4

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` Evidence of Reactions

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` The ability of an element to react is called the

elements activity.

` The more readily an element reacts the greateractivity it has.

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` A list organized by the ease at which certain

elements will undergo a chemical reaction.(p.266)

` The order is determined by single-replacementreactions.

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` Most Active

` Least Active` The most active element is placed at the top and

can replace each of the elements below it.

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` An element further down the list can only replace

an element below it not above it.

` The Activity Series will predict whether or not areaction will take place.

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` Al will replace Zn:

` 2Al (s) + 3ZnCl2(aq) 3Zn(s) + 2AlCl3 (aq)

`

Co will not replaceN

a` Co(s) + NaCl(aq) no rx.

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` Sample problem 8-6, p. 266

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ch. 8 - chemical equations and reactionsweb[1]

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