The standard enthalpy change of any reaction can be obtained from the standard enthalpies of formation ΔHf of the reactants and products.In the above thermochemical cycle, the enthalpy of the reaction ΔH is given byΔHf C2H5Cl(g) - ΔHf C2H4(g) - ΔHf HCl(g)= -109 - (-92.3) - (+52.2)= -68.9 kJmol-1
Determination of Enthalpy Change of a Reaction from Enthalpies of Formation Using Hess's Law
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Specification: OCR Chemistry A (H032), AS-level, 3.2.1 Enthalpy changes. Topic: Enthalpy.
Key terms in this lesson
- Enthalpy
- A measure of the total energy of a chemical system.
- Enthalpy change
- The heat energy that is transferred between the system and its surroundings during a process carried out at constant pressure.
More in Enthalpy
- Determining the Enthalpy Change of a Reaction
- Cooling Curves
- Average Bond Enthalpy
- Calculating Enthalpy Changes from Bond Enthalpies
- Limitations of Bond Enthalpy Calculations
- Hess's Law
- Determination of Enthalpy Change of a Reaction from Enthalpies of Combustion using Hess's Law
- Exam-style Question
All 19 lessons in Enthalpy · All OCR AS-level Chemistry topics