The net heat change in a chemical reaction is smae weather it takes place in one ste or several steps. This law is known as:
Correct answer: C. Hess's law
- A. First law of thermodynamics
- B. Henery's law
- C. Hess's law
- D. Joule's law
Explanation
Option A: The first law of thermodynamics states that energy can neither be created nor destroyed, only altered in form. Hence incorrect. Option B: Henry's law is a gas law that states that the amount of dissolved gas in a liquid is directly proportional to its partial pressure above the liquid. The proportionality factor is called Henry's law constant. Hence incorrect. Option C: Hess's law states that the overall change in enthalpy for a chemical reaction is equal to the sum of the enthalpy changes for each step. And this is independent of the path taken. Hence it is the correct option. Option D: Joule's law states that the amount of generated heat in a conductor carrying current is proportional to the square of the current flow through the circuit when the electrical resistance and current supply are constant. Hence incorrect.
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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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Related questions
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?
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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
Hess's law is analogous to:
Hess's law states that the enthalpy change of a reaction