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Chemical Reactions Chapter 2 Section 1
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Review… Chemical Bond is a force that holds two atoms together CHEMICAL REACTION A process in which one or more substance change to make one or more new substances
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Physical Background Physical Property: Characteristics of matter that can be seen through direct observations Density Melting point Boiling Point Physical Change: Change in which the identity of the substance does not change
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Chemical Background Chemical Property: characteristics that can only be observed when one substance changes into a different substance –Iron to Rust Chemical Change: New Substance is formed
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A Change of Properties The properties of these substances are very different from the starting substances In a chemical reaction –bonds are broken –atoms are rearranged –new bonds are formed
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Signs of a Chemical Reaction Gas Formation Solid Formation –Percipitate Energy Change –Endothermic –Exothermic Color change
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Chemical or Physical Glass Breaking Hammering wood together Burning Leaves Melting Ice Frying an egg Melting butter Bleaching your hair Fireworks Mixing salt with water
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Math Practice 1.3(2)= 2.4(2+3a)= 3.1(3a+4b)= 4.2(2a+3b+5c)=
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Chemical Formula A shorthand way to use chemical symbols and numbers to represent a substance Shows how many of each atom is present in a molecule –H2O–H2O
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Chemical Formula Shows how many of each atom is present in a molecule –3H 2 O Subscript 2 – (applies to symbol before it) Coefficient 3 – (applies to entire molecule)
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4 Mg: 4 Cr: 4 O:16 C: 30 H: 60 O:30 Mg:2 Cl:4 H:6 S:3 O:12 O:2 H:2 Cl:14 5 7 2 3 2
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Be Accurate Symbols can be mistaken!!
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Use chemical symbols and formulas as a shortcut to describe a chemical reaction Reactants = starting material Products = substances formed from a reaction C + O 2 CO 2 reactants before arrow products after arrow Chemical Equations
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Law of conservation of mass During a reaction, mass is neither created nor destroyed Equations must be balanced because atoms are neither created nor destroyed Mass of Reactants = Mass of Products
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Chemical Equation Shows the reaction between reactants and products Reactants-starting material Products-what is formed C + O 2 CO 2 C=1C=1 O=2O=2
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Balancing Chemical Equations
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Example: Mg + O 2 MgO Then all you do is list the atoms that are involved on each side of the arrow Mg + O 2 MgO Mg O Mg O
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[1] Just count up the atoms on each side Then start balancing: Mg + O 2 MgO Mg O 1 1 1 2 [2] The numbers aren’t balanced so then add Coefficient to make up for any shortages And adjust totals Mg + O 2 MgO Mg O 1 1 1 2 2 2 2 Mg O
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Mg + O 2 MgO Mg O 1 2 2 2 2 But the numbers still aren’t equal, so add another Coefficient 2 And adjust totals again NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS WE SAY THAT THE EQUATION IS BALANCED!! 2
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Try to balance these equations using the same method: [1] Na + Cl 2 NaCl [2] CH 4 + O 2 CO 2 + H 2 O [4] Al + O 2 Al 2 O 3 [3] Li + HNO 3 LiNO 3 + H 2
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[1] 2 Na + Cl 2 2 NaCl [2] CH 4 + 2 O 2 CO 2 + 2 H 2 O [4] 4 Al + 3 O 2 2 Al 2 O 3 [3] 2 Li + 2 HNO 3 2 LiNO 3 + H 2 Here are the answers: HOPE YOU’VE GOT THE IDEA… REMEMBER TO CHECK THAT YOU CAN DO ELECTROLYSIS EQUATIONS TOO
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