IB HL Chemistry | Chapter 5 Thermochemistry | Enthalpy
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Enthalpy
EnthalpyChapter 5: Energetics and ThermodynamicsIB Standard Level ChemistryEnthalpyYou know that enthalpy (H) is the heat or energy content in a system.A reactions reactants and products also have enthalpy.H = Hproducts Hreactants(i.e. final initial)
This is usually expressed as an overall enthalpy change, H.
SystemSurroundingsEnthalpy Changes: FormationHf is the energy change on forming a substance from its individual partsNa(s) + Cl2(g) -> NaCl(s)
+->Enthalpy Changes: CombustionHc is the energy change on completely combusting a substance2H2(s) + O2(g) -> 2H2O(s)
+->
+Enthalpy ChangesAlways include state symbols for enthalpy change equations
H can be positive or negativeIf H < 0, the products have less energy than the reactantsIf H > 0, the products have more energy than the reactants
Enthalpies of ReactionWhen H is positive, the reaction is endothermicThe system takes in energy, and the surroundings lose energyA thermometer will detect a decrease in energy
When H is negative, the reaction is exothermicThe system loses energy, and the surroundings gain energyA thermometer will detect an increase in temperature
QuestionUsing the values from the Data Booklet, write a formula for the combustion of hydrogen, along with its enthalpy value. State if it is endothermic or exothermic.