Answer
See answer below.
Work Step by Step
For ideal gases:
$\dfrac{P_1V_1}{T_1}=\dfrac{P_2V_2}{T_2}$
Eq. 7-33:
$s_2-s_1=c_v\ln\left(\dfrac{T_2}{T_1}\right)+R\ln\left(\dfrac{V_2}{V_1}\right)$
$s_2-s_1=c_v\ln\left(\dfrac{T_2}{T_1}\right)+R\ln\left(\dfrac{P_1T_2}{P_2T_1}\right)$
$s_2-s_1=c_v\ln\left(\dfrac{T_2}{T_1}\right)+R\ln\left(\dfrac{T_2}{T_1}\right)-R\ln\left(\dfrac{P_2}{P_1}\right)$
Since $c_p=c_v+R$
$s_2-s_1=c_p\ln\left(\dfrac{T_2}{T_1}\right)-R\ln\left(\dfrac{P_2}{P_1}\right)$
