Acetylene (C₂H₂) and nitrogen (N₂) both contain a triple bond, but they differ greatly in their chemical properties. (b) By referring to Appendix C, look up the enthalpies of formation of acetylene and nitrogen. Which compound is more stable?

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Identify the enthalpy of formation (\( \Delta H_f^\circ \)) for each compound from Appendix C.

Recall that the enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.

Understand that a more negative enthalpy of formation indicates a more stable compound, as it releases more energy upon formation.

Compare the \( \Delta H_f^\circ \) values of acetylene (C_2H_2) and nitrogen (N_2).

Determine which compound has a more negative \( \Delta H_f^\circ \) value to conclude which is more stable.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enthalpy of Formation

Enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It provides insight into the stability of a compound; lower enthalpy values indicate greater stability. For example, if acetylene has a higher enthalpy of formation than nitrogen, it suggests that nitrogen is more stable under standard conditions.

Triple Bonds

A triple bond consists of one sigma bond and two pi bonds, resulting in a strong interaction between two atoms. In acetylene (C2H2), the carbon atoms are connected by a triple bond, which contributes to its reactivity and energy content. In contrast, nitrogen (N2) also has a triple bond, but its stability is enhanced by the strong bond energy, making it less reactive than acetylene.

Chemical Stability

Chemical stability refers to the tendency of a compound to maintain its structure and resist change under various conditions. Factors influencing stability include bond strength, molecular structure, and enthalpy of formation. In this context, comparing the enthalpies of formation of acetylene and nitrogen helps determine which compound is more stable, with lower energy compounds being more stable.

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One scale for electronegativity is based on the concept that the electronegativity of any atom is proportional to the ionization energy of the atom minus its electron affinity: electronegativity = k1I - EA2, where k is a proportionality constant. (d) Use your result from part (c) to determine the electronegativities of Cl and O using this scale. Use your result to determine the electronegativity of Cl using this scale.

Textbook Question

Acetylene (C₂H₂) and nitrogen (N₂) both contain a triple bond, but they differ greatly in their chemical properties. (c) Write balanced chemical equations for the complete oxidation of N₂ to form N₂O₅(g) and of acetylene to form CO₂(g) and H₂O(g). Write a balanced chemical equation for the complete oxidation of acetylene to form CO₂(g) and H₂O(g).

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Textbook Question

Acetylene (C₂H₂) and nitrogen (N₂) both contain a triple bond, but they differ greatly in their chemical properties. (d) Calculate the enthalpy of oxidation per mole for N₂ and for C2H₂ (the enthalpy of formation of N₂O₅(g) is 11.30 kJ/mol).

Textbook Question

Acetylene (C₂H₂) and nitrogen (N₂) both contain a triple bond, but they differ greatly in their chemical properties. (e) Both N₂ and C₂H₂ possess triple bonds with quite high bond enthalpies (Table 8.3). Calculate the enthalpy of hydrogenation per mole for both compounds: acetylene plus H₂ to make methane, CH₄; nitrogen plus H₂ to make ammonia, NH₃.

Acetylene (C2H2) and nitrogen (N2) both contain a triple bond, but they differ greatly in their chemical properties. (b) By referring to Appendix C, look up the enthalpies of formation of acetylene and nitrogen. Which compound is more stable?

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Key Concepts

Enthalpy of Formation

Triple Bonds

Chemical Stability

Acetylene (C₂H₂) and nitrogen (N₂) both contain a triple bond, but they differ greatly in their chemical properties. (b) By referring to Appendix C, look up the enthalpies of formation of acetylene and nitrogen. Which compound is more stable?