Enthalpy (OCR A-Level Chemistry A): Flashcards

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Hess' Law and Enthalpy Cycles
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Hess' law statement

Total enthalpy change identical regardless of route taken

Principle Hess' law is based on

Law of conservation of energy

Enthalpy cycle

Diagram showing different routes from reactants to products

ΔfH∘\Delta_f H^\circ for elements in standard state

Always zero

ΔrH\Delta_r H formula using ΔfH∘\Delta_f H^\circ

∑ΔfH\sum \Delta_f H (products) −- ∑ΔfH\sum \Delta_f H (reactants)

ΔrH\Delta_r H formula using ΔcH∘\Delta_c H^\circ

∑ΔcH\sum \Delta_c H (reactants) −- ∑ΔcH\sum \Delta_c H (products)

Arrow direction in formation cycles

Upward from elements

Arrow direction in combustion cycles

Downward to combustion products

Common reference in formation cycles

Constituent elements

Multiply tabulated ΔH\Delta H values by

Stoichiometric coefficients from balanced equation

Explore OCR A-Level Chemistry A Revision Notes by Topics

Periodicity

Reactivity Trends

Enthalpy

Reaction Rates and Equilibrium

Explore OCR A-Level Chemistry A Model Answers by Topics

Periodicity

Reactivity Trends

Enthalpy

Reaction Rates and Equilibrium

Explore OCR A-Level Chemistry A Quizzes by Topics

Periodicity

Reactivity Trends

Enthalpy

Reaction Rates and Equilibrium

Explore OCR A-Level Chemistry A Exam Questions by Topics

Periodicity

Reactivity Trends

Enthalpy

Reaction Rates and Equilibrium

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