THIS IS 100 200 300 400 500 Chp. 13a Chp. 13b Chp. 13cChp. 14a Chp. 14b Leaders.
Chp 7.3 Energy Changes in Reactions
Transcript of Chp 7.3 Energy Changes in Reactions
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Energy Changes in Reactions���(Chp 7.3)
Chemical Energy • Is the energy stored in the chemical
bonds of a substance • Energy changes are determined by the
changes that occur in chemical bonding • Chemical reactions involve the
breaking of chemical bonds in the reactants and the formation of chemical bonds in the products
Chemical Bonds and Energy • Heat is a form of energy that can be released from a
chemical reaction • In a propane grill, a chemical reaction takes place that
produces the heat that cooks your food • The chemical equation for the combustion of propane
shows heat as one of the products of the equation C3H8 + 5O2 -----> 3CO2 + 4H2O + Heat
Breaking Bonds • Breaking bonds requires energy • Propane grills have an igniter which produces
the spark that provides enough energy to break the bonds of the reacting molecules. – The spark gets the reaction going
Forming Bonds • The formation of chemical bonds releases energy • For each molecule of propane burned, 3 molecules of
carbon dioxide and 4 molecules of water are formed. • So six C=O double bonds and eight O-H single bonds
form – The formation of these new bonds give off the heat
and light
Exothermic & Endothermic Reactions • During a chemical reaction, energy is
either released or absorbed
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Exothermic Reactions • A chemical reaction that releases energy to its
surroundings • The energy that is released as the products form
is greater than the energy required to break the bonds in the reactants
Endothermic Reactions • A chemical reaction that absorbs more energy from
its surroundings • More energy is required to break the bonds in the
reactions than is released by the formation of the products
Mercury (II) oxide + 181.7 kJ (energy) --> 2 mercury + O2
Conservation of Energy • The total amount of energy before and
after the reaction is the same • Exothermic – Chemical energy of reactants = heat + chemical energy of
products
• Endothermic – Heat + chemical energy of reactants = chemical energy of
products