CH 8 - CH 8: Chemical Reactions Renee Y. Becker CHM 1025...

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CH 8: Chemical Reactions Renee Y. Becker CHM 1025 Valencia Community College 1
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2 In a physical change , the chemical composition of the substance remains constant. Examples of physical changes are the melting of ice or the boiling of water. In a chemical change , the chemical composition of the substance changes; a chemical reaction occurs. During a chemical reaction, a new substance is formed. Chemical & Physical Changes
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3 Chemistry Connection: Fireworks The bright colors seen in fireworks displays are caused by chemical compounds, specifically the metal ions in ionic compounds. Each metal produces a different color Na compounds are orange-yellow Ba compounds are yellow-green Ca compounds are red-orange Sr compounds are bright red Li compounds are scarlet red Cu compounds are blue-green Al or Mg metal produces white sparks
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4 There are four observations that indicate a chemical reaction is taking place. 1. A gas is released . Gas may be observed in many ways in a reaction from light fizzing to heavy bubbling. Shown here is the release of hydrogen gas from the reaction of magnesium metal with acid. Evidence for Chemical Reactions
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5 2. An insoluble solid is produced . A substance dissolves in water to give an aqueous solution . If we add two aqueous solutions together, we may observe the production of a solid substance. The insoluble solid formed is called a precipitate . Evidence for Chemical Reactions
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6 3. A permanent color change is observed . Many chemical reactions involve a permanent color change. A change in color indicates that a new substance has been formed. Evidence for Chemical Reactions
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7 4. A heat energy change is observed . A reaction that releases heat is an exothermic reaction . A reaction the absorbs heat is an endothermic reaction . Examples of a heat energy change in a chemical reaction are heat and light given off. Evidence for Chemical Reactions
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A chemical equation describes a chemical reaction using formulas and symbols. A general chemical equation is: A + B C + D In this equation, A and B are reactants and C and D are products . We can also add a catalyst to a reaction. A catalyst is written above the arrow and speeds up the reaction without being consumed. Writing Chemical Equations
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This note was uploaded on 10/19/2011 for the course CHEM 1025 taught by Professor Smith during the Spring '10 term at Valencia.

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CH 8 - CH 8: Chemical Reactions Renee Y. Becker CHM 1025...

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