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

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

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  NCl3 Hr= 900 J 5. H2 + Cl2  HCl + 80J exo 6. C4H10 + O2 - 900J CO2 + H2O Fe + CuSO4 + 10J  Cu + FeSO4 8. CaCl2  Ca+2 + 2Cl-1 + 50J 9. P + Cl2 + 60J  PCl3 10. H2O(s)  H20 (l)

Thermochemical Equations and Stoichiometry smartboard

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

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 of H2O 1ᵒC you require 4.2J.

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

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

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)

Element Elemental State Hydrogen H2 Oxygen O2 Nitrogen N2 Chlorine Cl2 Carbon C (graphite) Fluorine F2 Metals M Eg. Formation reaction for NaHCO3 Na + H2 + C + O2  NaHCO3

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 of X: 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 ΔH solution: Heat of solution: The amount of heat absorbed/released when 1 mole of a substance dissolves

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

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

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

Smartbaord examples.