unit 5. converted a chemical reaction is a change in which one or more substances are converted...
DESCRIPTION
before The reactants are the substances that exist before the reaction after The products are the substances that exist after the reactionTRANSCRIPT
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INTRODUCTION TO
CHEMICAL EQUATIONS
Unit 5
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CHEMICAL REACTIONS• A chemical reaction
is a change in which one or more substances are converted into new substances
• Review: a substance is an element or a compound
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The reactants are the substances that exist before the reaction
The products are the substances that exist after the reaction
CHEMICAL REACTIONS
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CONSERVATION OF MASSLaw of Conservation of Mass: The total mass of the products must always equal the mass of the reactants
Mercury (II) oxide = oxygen + mercury
10.0g = 0.7g + 9.3g
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A chemical equation describes the chemical reaction using formulas and symbols (and usually coefficients)
Ca + O2 → CaO
CHEMICAL REACTIONS
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• Seven elements are always written as two atoms bonded together!
• When writing chemical equations, you will always write these elements with a subscript of a ‘2’
Br2 I2 N2 Cl2 H2 O2 F2
DIATOMIC ELEMENTS!
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CHEMICAL REACTION SYMBOLS
YieldsCoefficientSubscript
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Symbols for StateSolids: (s)Liquids: (l)Dissolved in water: (aq)Gases: (g)
2 Mg (s) + O2 (g) → 2 MgO (s)
CHEMICAL EQUATION SYMBOLS
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Coefficients represent the number of units of each substance that take part in the reaction
Al + O2 Al2O3
CHEMICAL EQUATIONS
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• Because mass must be conserved, coefficients are used to balance an equation
• The same number of atoms of each element must be on both sides of the equation
4 Al + 3 O2 2 Al2O3
CHEMICAL EQUATIONS
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BALANCING CHEMICAL EQUATIONS
Trial and Error Method!
Cu + O2 → Cu2O
Al + O2 → Al2O3
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BALANCING CHEMICAL EQUATIONS
N2 + H2 → NH3
Mg + P4 → Mg3P2
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BALANCING CHEMICAL EQUATIONS
Al(OH)3 + HBr AlBr3 + HOH
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BALANCING CHEMICAL EQUATIONS
NH4OH + H3PO4 (NH4)3PO4 + HOH