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Chemical Applications

Chemical Applications. Assignment 3 Endothermic and exothermic reactions. Chemical changes produce heat changes. You need to understand that: Chemical reactions either give out heat (exothermic) or, take in heat (endothermic). Keywords: energy, bonds,. Magnesium reacting with acid.

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Chemical Applications

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  1. Chemical Applications Assignment 3 Endothermic and exothermic reactions OCR_CD2_Endo and Exo reactions

  2. Chemical changes produce heat changes You need to understand that: Chemical reactions either give out heat (exothermic) or, take in heat (endothermic). Keywords:energy, bonds, OCR_CD2_Endo and Exo reactions

  3. Magnesium reacting with acid Thermit reaction Exothermic reactions increase the temperature. • Examples include: • Burning reactions including the combustion of fuels. • Detonation of explosives. • Reaction of acids with metals. OCR_CD2_Endo and Exo reactions

  4. Secondly… Endothermic reactions OCR_CD2_Endo and Exo reactions

  5. Endothermic reactions cause a decrease in temperature. OCR_CD2_Endo and Exo reactions

  6. Activity: • Calculate the Activation energy and the overall output energy for the following combustion reactions • It’s best to start by drawing a diagram on the molecules reacting Methane + Oxygen  Carbon Dioxide + Water CH4 + O2  CO2 + H2O OCR_CD2_Endo and Exo reactions

  7. Investigating exothermic and endothermic reactions • The assignment for this unit requires a thorough description of exo- and endo- thermic reactions. • Examples • Energy diagrams • Key phases: Activation energy, Energy of reactants, energy of products etc. OCR_CD2_Endo and Exo reactions

  8. Assignment details… Scenario … • We are a company making cold packs for sports injuries. • They also make heat packs for expeditions. • We have asked a chemical company to send us a list of reactions which produce a heat change to help us decide what to make our hot and cold packs from. • We need to investigate which reactions would be best to use to make our hot and cold packs. • You need to suggest reactants that would make effective heat / cold packs. OCR_CD2_Endo and Exo reactions

  9. Exo- and Endothermic Reactions

  10. Distinction theory: Assignment 3 BTEC Chemistry • Theory to help you: • Energy changes in reactions involve making and breaking bonds. • Energy is absorbed by reactants to break their bonds and then released by products when their bonds are made. • Each bond between atoms has its own amount of energy needed to make or break the bond. • If we know how much energy is needed to break the existing bonds and how much energy is released when making the new bonds then we can work out whether a reaction is exothermic or endothermic OCR_CD2_Endo and Exo reactions

  11. Burning… • When a hydrocarbon burns it joins with oxygen… Methane + oxygen →

  12. Burning… • When a hydrocarbon burns it joins with oxygen… Methane + oxygen → The heat you supply with a match Splits up the atoms… This bit needs energy, lets say 10 Joules

  13. Burning… • When a hydrocarbon burns it joins with oxygen… Methane + oxygen → → Carbon dioxide + water The atoms then recombine to make carbon dioxide and water When these atoms recombine, they release 15 Joules This bit needed 10 Joules…

  14. Task… • Calculate the energy released when hydrogen is burnt in air to produce water. Hydrogen + Oxygen  Water 2H2 + O2  2H2O Start by drawing a diagram of the atoms reacting...

  15. e.g. 2H2 + O22H2O More energy is made creating the bonds than is used breaking the bonds so the reaction is exothermic To break these bonds takes (2 X 436) + (1 X 498) = 1370 KJ/ mol To make these bonds produces (4 X -464) = -1856 KJ/Mol H H O H O H O H H O H + H H H O H O H OCR_CD2_Endo and Exo reactions

  16. Task… • Calculate the energy released when methane burns in oxygen • Bond strengths… • Extension – repeat for propane OCR_CD2_Endo and Exo reactions

  17. OCR_CD2_Endo and Exo reactions

  18. Assignment OCR_CD2_Endo and Exo reactions

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