Heat evolved or absorbed in a chemical reaction does not depend upon?
Correct answer: B. Pressure of reaction
- A. Amount of reactants
- B. Pressure of reaction
- C. Physical state of reactants and products
- D. Temperature
Explanation
The correct answer is Pressure of reaction. Enthalpy is a thermodynamic state function that represents the heat content of a system. Under constant pressure conditions, the change in enthalpy (ΔH) reflects the heat evolved or absorbed during a chemical reaction and is independent of the pressure at which the reaction occurs, as long as the initial and final states are the same. This is because enthalpy is determined by the internal energy, pressure, and volume of the system, which are all state properties.Amount of reactants: This affects the total enthalpy change because more reactants generally lead to a larger heat change. Thus, it does affect the heat evolved or absorbed.Physical state of reactants and products: Different physical states have different enthalpy values (e.g., the enthalpy of vaporization or fusion), so this factor also affects the heat change.Temperature: Changes in temperature can affect the enthalpy of a system, as it influences the energy levels and distribution of molecules, thereby affecting the heat evolved or absorbed.
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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