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Chemical Reactions Chapter 7
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The Nature of Chemical Reactions
Section 1
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Chemical Reactions Chemical Reaction: when a substance undergoes chemical changes, forming a new substance Cannot be reversed The new substance will have DIFFERENT chemical and physical properties than the original
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Chemical Reactions Some observations that suggest a chemical change has taken place… Heat, light or sound Production of a gas Formation of a precipitate (“stuff forming”) Change in color - This is not conclusive proof though, it needs to be proven that some new compound is present.
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Chemical Reactions Reactants: Starting materials in a reaction
Products: Ending materials in a reaction The products of a reaction are made up of the same number and type of atoms as the reactants, they have just been rearranged
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Chemical Reactions C6H12O6 + 6O2 6CO2 + 6H2O Glucose and oxygen react to form carbon dioxide and water Same number and kind of atoms on each side, just in different arrangements, it has changed into a different molecule.
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Chemical Reactions Chemical reactions involve breaking old bonds followed by the making of new ones Breaking bonds RELEASES energy Forming bonds REQUIRES energy Energy stored in bonds = chemical energy Activation Energy: The energy required to break enough bonds for a reaction to start
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Exothermic Reactions Reactions that RELEASE energy
More energy in the reactants than the products The extra chemical energy from the reactants is released as heat when the bonds in the products reform
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Endothermic Reactions
Reactions that ABSORB energy More energy needed to break the bonds than is released
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Chemical Equations section 2
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Remember! All MATTER and ENERGY are conserved, but they can change forms What goes in must come out, but it can be rearranged! You have to account for all the stuff that goes into the reaction
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Chemical Equations Chemical reactions are shown with chemical equations Reactants Products A chemical equation uses symbols to show the relationship between the reactants and products
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Balancing Equations An equation is balanced when the number of molecules/atoms in the reactants matches those in the products An equation is balanced by changing the ratios of molecules/atoms so each side has the lowest possible same whole number and type of atoms
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Balancing Equations A coefficient is a number that shows the relative amount of a compound in a reaction You CAN change the coefficient in front of any atom/molecule You CANNOT change the subscript (this would change the formula of the molecules)
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C6 H12 O6 + 6O2 6C + O2 6H2 O Carbon - 6 Carbon - 6 Hydrogen - 12 Hydrogen - 12 Oxygen - 18 Oxygen - 18
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Let’s Practice! _____H2 + _____ O2 ____ H2O
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Let’s Practice! ____ H2 + ____ N2 ____ NH3
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