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5. Thermodynamics and thermochemistry — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistry5. Thermodynamics and thermochemistry1 Mark
MCQ
The heat of formation is the change in enthalpy accompanying the formation of a substance from its elements at $298\, K $ and $1 \,atm$  pressure. Since the enthalpies of elements are taken to be zero, the heat of formation $(\Delta H)$ of compounds
  • A
    Is always negative
  • B
    Is always positive
  • ✓
    May be negative or positive
  • D
    Is zero
✓

Answer

Correct option: C.
May be negative or positive
c
Enthalpy of Formation : The heat evolved or absorbed when $1\, mole$ of a substance is formed from its constituent elements under constant pressure and temperature conditions is called enthalpy of formation.

It can be positive/negative or zero depends upon particular reaction.

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