Download - Chemical Change
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Chemical ChangeChapter 3
Section 3.1
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Identify important reactions in society Recognize and identify evidence for
chemical changes Differentiate between endothermic and
exothermic reactions Describe the Law of Conservation of Mass
Objectives
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What is the difference between a chemical and physical change?
◦ Chemical change- something new is created with its own unique properties
◦ Physical change- nothing new is created (just changing states) What are the three states?
To Start
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Which of the following are chemical changes? Physical changes?
Chemical or Physical?
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Reactant + reactant product(s) Products have different properties than
reactants◦ Properties include: state at RT, temperature,
melting point, color and density Includes a flow of energy
◦ IMPORTANT: drives chemical reactions Can be fast or slow
Chemical Change
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Batteries Combustion Engine Wine production Baking bread Photosynthesis Cellular respiration (making energy in our
bodies)
Examples of Chemical Reactions
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What are ways that we know a chemical change has occurred?◦ Formation of a gas (bubbles)
Air bag inflation in a car◦ Color change
Sugar and sulfuric acid◦ Formation of a precipitate (change in state)
Mixing silver nitrate with sodium chloride◦ Flow of energy (usually detected as a change in
temperature) Combustion (lighting a match)
Evidence of a Chemical Change
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What will happen when I add baking soda to vinegar in this beaker?
What will happen to the balloon placed over the top?
What gas is produced?
What other examples do we have of a formation of a gas?
Formation of a Gas: Demo
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Two types of energy changes:
◦ Exothermic- release of energy (*exit)◦ Endothermic- absorption of energy (*enter)
What change of temperature would you feel with each of these processes?
Can physical changes be exothermic and endothermic? Why or why not?
Energy Changes
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Release energy, usually as:◦ heat (flame)◦ light (bioluminescence) ◦ Electricity (battery)
Important ex.: Combustion◦ What is combustion?
Combustion- oxygen reacts rapidly with another substance, releasing energy (burning)◦ 2C6H14(l) + O2(g) 12CO2(g) + 14H2O(g) + energy◦ (Combustion of hexane)
Exothermic Reactions
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Absorb energy Ex. Cold packs- squeeze package, breaks
pack inside which keeps chemicals separate; absorb energy and whole mixture cools down
Ex. Photosynthesis◦ Energy + 6CO2(g) + 6H2O(l) C6H12O6(aq) + 6O2(g)
Endothermic Reactions
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They may be endothermic or exothermic They are almost always helped by enzymes
(biological catalysts) Catalysts are chemicals that speed up a
reaction but are not used up by it. Photosynthesis and Cellular Respiration
Biochemical Reactions
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Developed by Antoine Lavoisier Total mass of the reactants equals the
total mass of the products Using this, we can deduce that:
◦ ** total # of atoms present before a reaction equals the total # of atoms after a reaction
Law of Conservation of Mass
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If I get 13 g of H2O and 15 g of NaCl from the reaction of HCl and NaOH, how much NaOH did I use, if I used 10 g of HCl?
HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)
10g ? 13g 15g
Answer: 18 g
Example