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Thermochemistry

Thermochemistry. New unit. Thermochemistry. EXOTHERMIC Reaction : a reaction that releases heat to the surroundings temp of surroundings goes up ENDOTHERMIC Reaction : a reaction that absorbs heat from the surroundings temp of surroundings goes down.

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Thermochemistry

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  1. Thermochemistry New unit

  2. Thermochemistry EXOTHERMIC Reaction: a reaction that releases heat to the surroundings temp of surroundings goes up ENDOTHERMIC Reaction: a reaction that absorbs heat from the surroundings temp of surroundings goes down

  3. Graphically Energy ProfilesEnergy vs. Reaction Pathway (as the reaction proceeds) EXOTHERMIC Reaction Go to smartboard ‘EXO’ • A + B C + D + Δ HR • A + B - Δ HRC + D • A + B C + D Δ HR < 0 (negative) ENDOTHERMIC Reaction Go to smartboard ‘ENDO’ • P + W G + T -Δ HR • P + W + Δ HRG + T • P + W G + T Δ HR > 0 (positive)

  4. Identify the following reactions as EXO or ENDO • CH4 + O2 – 600J  CO2 + H2O Exo • C3H8 + O2 CO2 + H2O HR = -500J Endo • CO2 + H2O  O2 + C6H12O6 -1800J endo 4. N2 + Cl2  NCl3Hr= 900 J endo 5. H2 + Cl2  HCl + 80J exo 6. C4H10 + O2 - 900J CO2 + H2O exo • Fe + CuSO4 + 10J  Cu + FeSO4 endo 8. CaCl2  Ca+2 + 2Cl-1 + 50J exo 9. P + Cl2 + 60J  PCl3 endo 10. H2O(s)  H20 (l) endo

  5. Thermochemical Equations and Stoichiometry smartboard

  6. Homework: Finish Q’s if not done Read text pg. 298 – 300 Define: Thermochemistry Thermal Energy Chemical System Surroundings Open system Closed system

  7. Heat: Q – measured in Joules Specific Heat Capacity: c • A physical property • The amount of heat (Joules) required to raise the temp of 1g of a given substance 1ᵒC • ex.. cH2O = 4.2J/gᵒC this means… if you want to raise the temp of 1g ofH2O1ᵒC you require 4.2J.

  8. Suppose you want to raise the temp of 100g of H2O 1ᵒC NOT FINISHED!!!!

  9. Thermochemistry cont’d ΔHR = The Heat of Reaction: • The amount of heat (J) absorbed/released in a given reaction • Follow stochiometry Eg. smartboard

  10. Types of Reactions • Combustion Reactions: a substance is burned (reacted in O2) • Formation Reaction: a substance is formed (produced) from its elements in their elemental state. • Metals – atoms (copper is Cu)

  11. Eg. Formation reaction for NaHCO3 Na + H2 + C + O2 NaHCO3

  12. ΔHcombustion of ‘x’: Heat of Combustion of X: • the amount of heat absorbed or released when 1 MOLE of a given subsance (x) burns (reacts in oxygen). J/mole ΔHformation ofX: Heat of Formation of X: • The amount of heat absorbed or released when 1 mole of a given substance (X) is formed from its elements in their elemental states. J/mole ΔHsolution: Heat of solution: • The amount of heat absorbed/released when 1 mole of a substance dissolves

  13. ΔHneutralization:Heat of Neutralization The amount of heat absorbed/released when 1 mole of a substance is neutralized J/mole ΔHdissociation: Heat of Dissociation: The amount of heat absorbed/released when 1 mole dissociates (breaks down into its atoms) J/mole Go to smartboard

  14. WRIGHTS Method: Calorimetry Measuring heats of reaction (ΔHR) The reaction is carried out in a reaction vessel. The amount of heat absorbed / released is measured by analysing what happens to the surroudings and the vessel. thermometer Reaction Vessel water

  15. Apply 1st Law of Thermodynamics Energy (heat) is neither created nor destroyed Qabsorbed/released = Q released / absorbed by the bythe reactionsurroundings Det. ΔHR using calorimietry is applying the 1st Law of Thermodynamics Surroundings  calculate Q using Q = mcΔt

  16. Smartbaord examples.

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