Enthalpy change can be_________________?
Correct answer: C. both A and B
- A. calculated by Hess law
- B. can be measured by calorimeter
- C. both A and B
- D. none
Explanation
An enthalpy change can be obtained experimentally from heat measurements in a calorimeter or calculated indirectly using Hess's law by combining known thermochemical equations. Students may choose only a or b when they treat calculation and measurement as alternatives rather than two valid methods.
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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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More Hess's Law questions
Given that C + O2 gives CO2 has an enthalpy change of minus 393 kJ per mole, and CO + half O2 gives CO2 has an enthalpy change of minus 283 kJ per mole, the enthalpy of formation of carbon monoxide is
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The net heat change in a chemical reaction is the same whether it is brought about in two or more different ways in one or several steps. This is known as:
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