Investigating Chemical Reactions

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Investigating Chemical Reactions
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• All chemical reactions involve the
• release
• or
• Absorption of energy.
• Energy can be in the form of
• heat, light, electricity and sound.
• Energy-releasing reactions are called
• exothermic.
• An example would be an explosion.

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• In an exothermic equation
• the energy
• Is written on the
• Product side
• Ex
• C6H12O6 O2 ? CO2 H2O Thermal
• energy

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• Energy-absorbing reactions are
• endothermic.
• An example would be cooking, or cold packs.
• Chemists classify reactions to make it easier to
  predict the products of reactions.

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Synthesis Reactions(also called Combination or
Composition Reactions)

• General Equation
• X Y ? XY
• Example
• 2H2 (g) O2 (g) ? 2H2O (l) thermal
  energy

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Decomposition Reactions

• General Equation
• XY ? X Y
• Example
• 2H2O (l) thermal ?2H2 (g) O2 (g)
• energy

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• Practice Questions
• Identify each of the following reactions as
  exothermic or endothermic, and indicate the type
  and balance the equation.

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• thermal energy N2(g) O2(g) ? NO2(g)
• endothermic or exothermic?
• endothermic
• Type and balanced equation
• thermal energy N2(g) 2O2(g) ? 2NO2(g)
• Synthesis Chemical Reaction

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• Na(s) Cl2(g) ? NaCl(s) thermal energy
• endothermic or exothermic?
• exothermic
• Type and balanced equation
• 2Na(s) Cl2(g) ? 2NaCl(s) thermal energy
• Synthesis Chemical Reaction

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• thermal energy CH3CH2OH(l) ? C(s) H2(g)
  O2(g)
• exothermic or endothermic?
• endothermic
• balanced equation
• thermal energy 2CH3CH2OH(l) ? 4C(s) 6H2(g)
  O2(g)
• Decomposition Chemical Reaction

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• Write skeleton equations for the following. Then
  tell if the reaction is synthesis or
  decomposition. Finally, balance the equation.

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• calcium oxygen gas ? calcium oxide
• skeleton equation
• Ca O2 ? CaO
• synthesis or decomposition?
• Synthesis Chemical Reaction
• Balanced equation
• 2Ca O2 ? 2CaO
• Balanced chemical equation
• 2Ca(s) O2(g) ? 2CaO(s)

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• copper(II) oxide ? copper oxygen gas
• skeleton equation
• CuO ? Cu O2
• synthesis or decomposition?
• Decomposition Chemical Reaction
• Balanced equation
• 2CuO ? 2Cu O2
• Balanced chemical equation
• 2CuO(s) ? 2Cu(s) O2(g)

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• More work/
• Homework
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• and
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