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What are the characteristics of enthalpy? |
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Answer» Solution :CHARACTERISTICS of enthalpy: (i)Enthalpy is a thermodynamic PROPERTY of a system. Enthalpy H is defined as sum of the internal energy (U) of a system and the product of pressure and volume of the system. That is, H=U + PV (ii)Enthalpy is a state FUNCTION which depends entirely on the state functions T,P and U . (iii)Enthalpy is usually expressed as the change in enthalpy (`DeltaF`) for a process between initial and final states. (iv)At constant pressure, the heat flow (q) for the process is equal to the change in enthalpy which is defined by the equation. `DeltaH=q_P` (v) In an endothermic reaction heat is absorbed by the system from the surroundings that is q > 0 (positive). Therefore, at constant T andP, by the equation above, if q is positive then `DeltaH` is also positive. (vi) In an exothermic reaction heat is EVOLVED by the system to the surroundings that is, q<0 (negative). If q is negative , then `DeltaH` will also be negative (vii)Unit of enthalpy is KJ `mol^(-1)` |
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