M2_2-student - Unit 2 How do we analyze chemical change?...

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Chemistry XXI Unit 2 How do we analyze chemical change? Module 2: Tracking Energy Central goal: To make qualitative and quantitative predictions about the amount of energy absorbed or released during a chemical reactions based on the nature of the chemical bonds in the molecules of reactants and products.
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Chemistry XXI The Challenge Modeling How do I explain it? We take advantage of chemical changes to generate most of the energy that we use in our daily lives, from fueling our cars to keep ourselves alive. What models can help us explain and predict energy transfer during a chemical reaction? What structural features of chemical substances can be used to make such predictions?
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Chemistry XXI Energy Transfer As we have seen, a common signature of a chemical change is the release or absorption of energy. Surroundings Surroundings System System heat q q > > 0 0 The system absorbs energy ENDOTHERMIC Surroundings Surroundings System System heat EXOTHERMIC q q < < 0 0 The system releases energy Heat
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Chemistry XXI Exothermic or Endothermic Combustion reactions are prototypical examples of exothermic processes: + ENERGY The decomposition of stable compounds, + ENERGY Let’s Think How do you explain the differences?
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Chemistry XXI The amount of energy released or absorbed in a chemical reaction depends on the nature of the reactants and products involved. Why is energy released in some cases and absorbed in others? Why is energy involved? How can we predict how much energy will be released or absorbed? What does energy transfer tell us about the properties and behavior of chemical substances? Central Questions
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Chemistry XXI A Chemical Model The transfer of energy during chemical reactions can be explained using the following model: 1. Pairs of atoms in molecules are attracted to each other through forces that we call covalent bonds .” The formation of these bonds is induced by electrostatic attraction between electrons and protons in the different atoms.
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Chemistry XXI Other Interactions Protons and electrons have an additional property called “ spin.
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This note was uploaded on 04/09/2009 for the course CHEM 151 taught by Professor Staff during the Fall '08 term at University of Arizona- Tucson.

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M2_2-student - Unit 2 How do we analyze chemical change?...

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