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Energy and Chemical Reactions

Energy and Chemical Reactions. E th E ph E ch. Energy Bar Graphs. Energy bar graphs account for energy storage. E th Kinetic energy E ph Phase energy E ch Chemical energy. E th E ph E ch. E th E ph E ch. E th E ph E ch. States of Matter.

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Energy and Chemical Reactions

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  1. Energy and Chemical Reactions

  2. Eth Eph Ech Energy Bar Graphs • Energy bar graphs account for energy storage Eth Kinetic energy Eph Phase energy Ech Chemical energy

  3. Eth Eph Ech Eth Eph Ech Eth Eph Ech States of Matter Solid Liquid Gas

  4. Eth Eph Ech Eth Eph Ech Q Heating a Liquid • Heating a liquid makes the particles move faster: Cold Hot

  5. Eth Eph Ech Eth Eph Ech Q Melting Ice • Heating causes a phase change Ice Water

  6. Chemical Energy Ech • Ech is the energy stored in the new arrangement of atoms • Reactions may be endothermic (absorb heat) or exothermic (release heat) • In energy diagrams we will disregard Eph to keep things simple

  7. Endothermic reaction • Heating the system increases Eth of reactant molecules (making them sufficiently energetic to produce reaction.) • During collisions, energy is transferred from Ethto Ech as products are formed. • The resulting system is cooler- requires continued heating to bring Eth back up to level required to sustain reaction

  8. Eth Eph Ech Eth Eph Ech Eth Eph Ech Endothermic reaction Heated initial Initial Final Q

  9. Endothermic Reaction • Energy term shows up on the left hand side of the equation: • Energy + CaCO3 CaO + CO2 • Typically shown as

  10. Exothermic reaction • During collisions, energy is transferred from Ech to Eth as products are formed that store less energy. • The resulting system is hotter. • Energy flows out of the system until thermal equilibrium is reached.

  11. Eth Eph Ech Eth Eph Ech Eth Eph Ech Exothermic reaction Heated final Initial Final Q

  12. Exothermic Reaction • Energy term shows up on the right hand side of the equation: • 2H2(g) + O2(g)  2H2O(g) + 483.6 kJ • Typically shown as

  13. Steps to drawing energy bar graphs • Write the balanced chemical equation with the energy term on the correct side of the equation. • Energy on right – exothermic – start with a high Ech and go from initial to heated final to final (low Ech) • Energy on left – endothermic – start with a low Ech and go from initial to heated initial to final (high Ech)

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