Question: An ideal gas, which is initially at a pressure of 4.05 atm and a temperature of 355 K is permitted to expand adiabatically to 1.51 times its initial volume. A. Find the final pressure if the gas is monatomic. I was thinking [tex]P_i \cdot V_i = P_f \cdot V_f[/tex]. But, I made no use of the information that the gas is monatomic. Later on, a question asks for the final pressure if the gas is diatomic. Well, my starting point wouldn't distinguish between the two, so it's not right.