Nature of energy function as extensive property - Thermodynamics

Q.  Which among the following statements are correct?
(1) Energy is an extensive property
(2) Specific energy is an extensive property
(3) Energy is a point function
(4) Heat capacity is an extensive property

- Published on 21 Aug 15

a. Statement (1), (2) and (3)
b. Statement (1), (3) and (4)
c. Statement (2), (3) and (4)
d. Statement (1), (2), (3) and (4)

ANSWER: Statement (1), (3) and (4)
 
We know that, when a system changes from state 1 to state 2, the change in internal energy (ΔE) of the state 2 is same as that of the state 1. Therefore value of internal energy of the system is independent of the path followed by the system. It has a fixed value along the path, therefore energy is the point function [statement (3) is correct]. But energy changes with mass of the body, therefore it is an extensive property [statement (1) is correct]. Specific energy is the energy of the system per unit mass of the system, therefore it will become intensive property [statement (2) is wrong]. Heat capacity is the product of specific heat and mass of the body. It depends on mass of the system, therefore heat capacity is an extensive property.

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