Question

A block of copper (SL model) is subjected to a change of state. The process is isentropic (that is, entropy does not change. Which of the following statements best describe the change of state. C. u is constant E. h is constant A. No change at all B. T is constant D. B and C

Answer 1

To develop this problem it is necessary to apply the definitions of entropy change within the bodies

The change of entropy in copper would be defined as

`\Delta S= (\delta Q)/(T)`

Where,

Q= Heat exchange

T = Temperature

For an incompressible substance, the change in the heat exchange is defined as

`\Delta Q =mcdT`

Where,

m = Mass

c = Specific heat

Replacing in our equation we have that

`\Delta S = (mcdT)/(T)`

`\Delta S = mc ln (T_f)/(T_i)`

Since
`\Delta S = 0`, then

`mcln(T_f)/(T_i) = 0`

`T_f = T_i`

In this way for the change of enthalpy and internal energy you have to

`\Delta U = \Delta h = mc\Delta T = mc(T_f-T_i)`

As
`Tf_= T_i`, then

`\Delta U = 0, \Delta H = 0`

Therefore the correct option is A. No change at All