chemical reactions
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Chemical Reactions
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Chemical reaction
• a chemical change
• bonds of reactants are broken and bonds of product are formed
reactants products(yield or make)
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• when some chemicals come into contact with each other, they break apart, join, or rearrange to form new chemicals (always to become more stable)
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Evidence of Chemical Rxn
• change in color (unexpected)
• change in temperature
• change in smell
• change in taste
• formation of a precipitate (appears cloudy)
• production of a gas (bubbles)
• production of heat, light, sound
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Chemical equations
• shorthand representations of chemical reactions
H2 + O2 H2O
(skeleton equation)
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Parts of a chemical equation . . .
• Reactants the elements or compounds that enter into a reaction
• Products are the elements or compounds that are formed as a result of a chemical reaction
• Arrow means yields, produces or forms
reactants products
yield
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Formula Equation
2 H2 (g) + O2 (g) 2 H2O (l)
• includes states of matter – (s) – solid– (l) – liquid– (g) – gas– (aq) – aqueous
• chemical equation must be balanced
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Word equation
hydrogen gas and oxygen gas form liquid water
2 H2 (g) + O2 (g) 2 H2O (l)
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Types of Chemical Reactions
1. Synthesis
2. Decomposition
3. Double Replacement
4. Single Replacement
5. Combustion
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1. Synthesis
A + B AB
• two or more substances react to form a single product
• example:
2 H2 (g) + O2 (g) 2 H2O (l)
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2. Decomposition
AB A + B
• a single compound breaks down into two or more substance
• example:
2 H2O (l) 2 H2 (g) + O2 (g)
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3. Single Replacement
A + BC AC + B
• the atoms of one element replace the atoms of another element in a compound
• example:
Zn (s) + Cu(NO3)2 (aq) Zn(NO3)2 (aq) + Cu (s)
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4. Double Replacement
AB + CD AD + CB
• metal cations exchange position between two compounds (dissolved in water)
• example:
AgNO3(aq) + NaCl (aq) AgCl (aq) + NaNO3(aq)
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5. Combustion
reactant(s) + O2 product(s)
• oxygen combines with a substance and releases energy (heat & light)
• example:
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l)
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What is the purpose of balancing chemical equations?
• The Law of Conservation of Mass states that matter is neither created nor destroyed during a chemical reaction. Therefore, when writing a chemical equation, the reactants must be equal to the products. So you must add any necessary coefficients to show that matter is conserved.
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METAL ACTIVITY SERIES
• During a Single Replacement reaction, a metal will not always replace another metal. This is because metals differ in their reactivities.
MOSTACTIVE
FrLiRbKCaNaMgZnFeNiSnPbCuAgPtAu
LEASTACTIVE
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• For example: Francium (Fr) is the most active metal on the table. It will replace (or kick out) any other metal. – NOTE: it’s the highest on the Activity Series list.
• So in the reaction below, the Fr metal with replace the Fe in the iron (II) chloride, resulting in pure iron metal as a product.
2 Fr + FeCl2 2 FrCl + Fe
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A Metal Activity Series helps you determine if a reaction will occur.
Au + FeCl2 no reaction
* gold is one of the least active metals, so it will not be able to replace (kick out) the iron metal, and the reaction will not take place.
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2 Al + 3 FeCl2 2 AlCl3 + 3 Fe
* Al is more reactive than iron, so it will replace (kick out) the iron metal, and the reaction will take place.
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Write out and balance the following
• Sulfur solid reacts with iron solid to form solid iron(III) sulfide.
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Magnesium metal reacts with hydrochloric acid to form
magnesium chloride solution and hydrogen gas.
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Oxygen gas reacts with solid copper metal to form copper(II)
oxide solid.
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Oxygen gas reacts with hydrogen gas to form liquid water.
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Hydrogen gas and aluminum chloride solution are produced when solid aluminum is reacted
with hydrochloric acid.
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Answer Key
• 3S (s) + 2Fe(s)------> Fe2S3(s)
• Mg(s) + 2HCl(aq)------> MgCl2(aq) + H2(g)
• O2(g) + 2Cu(s)------> 2CuO(s)
• 2H2(g) + O2(g)------> 2H2O(l)
• 2Al(s) + 6HCl(aq)------> 3H2(g) + 2AlCl3(aq)
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Try the followingWrite out the formula and balance.
• Dinitrogen pentoxide gas in the presence of a platinum catalyst and high enough temperature forms nitrogen gas and oxygen gas.
• Sulfur solid reacts with iron solid to form solid iron(III) sulfide.
• Hydrogen gas and iron(III) oxide powder react to form liquid water and solid iron powder.
• Magnesium metal reacts with hydrochloric acid to form magnesium chloride solution and hydrogen gas.
• Magnesium sulfide solid and hydrochloric acid react to form hydrogen sulfide gas and magnesium chloride solution.
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Key
• 2N2O5(g)------> 2N2(g) + 5O2(g)
• 3S (s) + 2Fe(s)------> Fe2S3(s)
• 3H2(g) + Fe2O3(s)------> 3H2O(l) +2Fe(s)
• Mg(s) + 2HCl(aq)------> MgCl2(aq) + H2(g)
• MgS(s) + 2HCl(aq)------> MgCl2(aq)+ H2S(g)
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Finding Formula Mass
• H3PO4
• AlCl3
• K2C4H4O6
• N2O5
• K3SO4
• Nd2O3