The net enthalpy change in a chemical reaction is same whether it is brought about in two or more different ways in one or several steps. It is known as:
Correct answer: C. Hess's law
- A. Joule's law
- B. Law of conservation of energy
- C. Hess's law
- D. Henry's law
Explanation
According to Hess's law, the thermal effects of a reaction depends upon the initial and final conditions of the reacting substances. It does not depend upon the immediate steps.
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About Hess's Law
Hess's law states that the enthalpy change of a reaction is independent of the route because enthalpy is a state function. Calculations involve reversing and adding thermochemical equations, using standard enthalpies of formation or combustion, and finding an unknown reaction enthalpy without confusing enthalpy change with reaction rate.
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The standard enthalpy changes of formation of iron (II) oxide, FeO(s), and aluminum oxide, Al2O3(s) are -266 kJ mol-1 and -1676 kJ mol-1 respectively. What is the enthalpy change under standard conditions for the following reaction? 3FeO(s) + 2Al(s) → 3Fe(s) + Al2O3(s)
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