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Chapter 10: Problem 9

The enthalpies of elements in their standard states are taken as zero. Thus, the enthalpy of formation of a compound (a) will always be positive (b) will always be negative (c) may be positive or negative (d) will always be zero

Short Answer

Expert verified
The standard enthalpy of formation of a compound may be either positive or negative (option (c)), depending on if the reaction is endothermic (absorbs heat) or exothermic (releases heat).

Step by step solution

01

Comprehend the definition of Standard Enthalpy of Formation

It is important to know that the standard enthalpy of formation, ΔH⁰f, is the amount of energy absorbed or released when one mole of a substance is formed from its constituent elements in their most stable form at standard conditions (1 bar or 1 atm pressure and 298K).
02

Understanding the sign convention

The sign of ΔH⁰f depends on whether the process absorbs or releases heat. If heat is absorbed during the reaction (endothermic process), ΔH⁰f is positive. Conversely, if heat is released (exothermic process), ΔH⁰f is negative.
03

Recognize Various Scenarios

Most compounds have either positive or negative ΔH⁰f, not zero, because they require or release energy when forming from their constituent elements. So the ΔH⁰f is not always positive, always negative, or always zero. Hence, the ΔH⁰f of a compound may be positive or negative based on the nature of the reaction whether it's endothermic or exothermic.

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Most popular questions from this chapter

The equations showing the effect of temperature change on the heat of reaction is known as (a) Arrhenius equation (b) Kirchhoff's equation (c) Ostwald's equation (d) none of these

Thermochemistry is the study of (a) heat changes accompanying chemical reactions (b) net entropy change in a reaction (c) net free energy change in a chemical reaction (d) none of these

"The resultant heat change in a chemical reaction is the same whether it takes place in one or several stages." This statement is called (a) Le-Chatelier's principle (b) Hess's law (c) Lavoisier-Laplace law (d) Joule-Thomson effect

Standard heat of formation of an element is (a) infinite (b) zero (c) \(100 \mathrm{~kJ}\) (d) \(200 \mathrm{~kJ}\)

The heat of neutralisation is maximum for the reaction (a) \(\mathrm{NaOH}\) and \(\mathrm{HCl}\) (b) \(\mathrm{NaOH}\) and \(\mathrm{CH}_{3} \mathrm{COOH}\) (c) \(\mathrm{HCl}\) and \(\mathrm{NH}_{4} \mathrm{OH}\) (d) \(\mathrm{NH}_{4} \mathrm{OH}\) and \(\mathrm{CH}_{3} \mathrm{COOH}\)
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