What is the standard enthalpy change of formation for a pure element in its standard state?

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Study for the Honors Chemistry Exam with flashcards and multiple choice questions. Enhance your understanding with detailed explanations and hints. Prepare to excel in your exam!

Multiple Choice

What is the standard enthalpy change of formation for a pure element in its standard state?

Explanation:
The standard enthalpy of formation uses a zero reference for elements in their standard states. When you form 1 mole of a pure element from its elements in their standard states, nothing chemically changes—the element is already in its standard state at 1 atm and 298 K—so no heat is absorbed or released. That’s why this enthalpy change is defined as zero for any element in its standard state, providing a consistent baseline for comparing formation enthalpies. Examples like H2, O2, N2, and carbon as graphite all have ΔHf° = 0.

The standard enthalpy of formation uses a zero reference for elements in their standard states. When you form 1 mole of a pure element from its elements in their standard states, nothing chemically changes—the element is already in its standard state at 1 atm and 298 K—so no heat is absorbed or released. That’s why this enthalpy change is defined as zero for any element in its standard state, providing a consistent baseline for comparing formation enthalpies. Examples like H2, O2, N2, and carbon as graphite all have ΔHf° = 0.

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