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:
Correct answer: B. Hess's law
- A. Henry's law
- B. Hess's law
- C. Joule's principle
- D. Dalton's law
Explanation
Hess's Law is a fundamental principle in thermochemistry, asserting that the total enthalpy change during a chemical reaction is the same regardless of the number of steps in which the reaction is carried out, because enthalpy is a state function. This means that it depends only on the initial and final states of the system, not on the path taken.Henry's law, Dalton's law, and Joule's principle all deal with different principles: Henry's law is about gas solubility in liquids, Dalton's law is about partial pressures in gas mixtures, and Joule's principle is about the conversion of electrical energy to heat in conductors. None of these involve the calculation of enthalpy changes in chemical reactions.
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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
The ΔHof for CO2(g), CO(g) and H2O(g) are −393.5, −110.5 and −241.8 kJ mol−1 respectively. The standard enthalpy change (in kJ) for the reaction: CO2(g) + H2(g) → CO(g) + H2O(g) is :
Enthalpy change can be_________________?
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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Combustion of graphite to form CO2 can be done by two ways. Reactions are given as follows: 1.C + O2 -> CO2 ∆H = -393.7 kJ mol-12.C + ½O2 -> CO ∆H = ?3.CO + ½O2 -> CO2 ∆H = -283 kJ mol-1What will be the enthalpy of the formation of CO?
Hess's law is analogous to: