What is not correct about ΔHr :
Correct answer: B. It is always negative
- A. Its value gives an idea about the relative stability of reactants and the products
- B. It is always negative
- C. Value depends upon nature of bonds
- D. Its value may be negative or positive
Explanation
The standard enthalpy of formation of a compound is the amount of heat absorbed or evolved when one mole of compound is formed from its elements under standard conditions. It may be +ve or -ve.The standard enthalpy of formation provides a measure of the stability and energy content of a compound. A negative value for ΔH°f indicates that the compound is more stable than its constituent elements, meaning energy is released during the formation process (exothermic reaction). Conversely, a positive value for ΔH°f indicates that the compound is less stable than its constituent elements, meaning energy is absorbed during the formation process (endothermic reaction).
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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