Oxygen gas having a volume of 784 cm3 at 23.3°C and 1.03 x 105 Pa expands until its volume is 1170 cm3 and its pressure is 1.07 x 105 Pa. Find (a) the number of moles of oxygen present and (b) the final temperature of the sample. (Unit kelvin, K, for part (b).)

Question

drwls · Accepted Answer

Use the perfect gas law to get the number of moles, n. You can use initial condition values of p, V and T . The inital T is 296.5 K, V is 0.784 l and p = 1.017 atm. R = 0.08205 l-atm/mole

n = PV/RT = 0.0328 moles

The temperature after expansion depends upon the type of expansion. Usually an isentropic expansion is assumed, with the gas doing work while it pushes against an external boundary or gas. If it expands into a larger volume that had been previously empty, the gas temperature will not change.

For an isentropic expansion of a diatomic gas,
T^(5/2) * V = constant

The 5/2 exponent equals 1/[gamma - 1].
gamma = 1.4 for diatomics
(T'/296.5)^2.5 = 784/1170 = 0.670
T'/296.5 = 0.852
t' = 252.6 K = -20.6 C

sweety · Answer

thank u so much for the help

drwls · Answer

T' is supposed to be the final temperature