ANS:A - Kirchoffs

Kirchhoff's equation, also known as Kirchhoff's law of thermochemistry, relates changes in enthalpy (Δ𝐻ΔH) to changes in temperature for a chemical reaction. It's often used to estimate the change in enthalpy at a different temperature if the enthalpy change at a known temperature is given. Mathematically, Kirchhoff's equation is given by: Δ𝐻new=Δ𝐻known+∫𝑇known𝑇new𝐶𝑝(𝑇) 𝑑𝑇ΔHnew​=ΔHknown​+∫Tknown​Tnew​​Cp​(T)dT Where:

• Δ𝐻newΔHnew​ is the enthalpy change at the new temperature 𝑇newTnew​,
• Δ𝐻knownΔHknown​ is the enthalpy change at the known temperature 𝑇knownTknown​,
• 𝐶𝑝(𝑇)Cp​(T) is the molar heat capacity of the system at temperature 𝑇T, and
• ∫𝑇known𝑇new𝐶𝑝(𝑇) 𝑑𝑇∫Tknown​Tnew​​Cp​(T)dT represents the integral of the molar heat capacity over the temperature range from 𝑇knownTknown​ to 𝑇newTnew​.

Kirchhoff's equation assumes that the molar heat capacity (𝐶𝑝Cp​) of the system remains constant over the temperature range of interest. This assumption is often valid for small temperature changes but may not hold for larger temperature ranges where 𝐶𝑝Cp​ might vary significantly.