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

$\Delta S= \frac{\delta Q}{T}$

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

$\Delta S = \frac{mcdT}{T}$

$\Delta S = mc ln \frac{T_f}{T_i}$

Since  $\Delta S = 0$, then

$mcln\frac{T_f}{T_i} = 0$

$T_f = T_i$

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