Initial Conditions:
Volume = V1 = 246 ml
Temperature = T1 = 0 °C = 273.25 K
Pressure = P1 = 1 atm
(Since the problem says that the gas is at STP which means standard conditions of temperature and pressure and they are 1 atm and 0 °C)
Final conditions:
Volume = V2 = 225 ml
Temperature = T2 = ?
Pressure = P2 = 1.20 atm
We are looking for the change in temperature, and the conditions of pressure and volume are changing also. We have to use the combined law of the ideal gases:
P1 * V1 / T1 = P2 * V2 / T2
If we solve it for T2 (which is our unknown):
T2 = P2 ¨*V2 * T1 / ( P1 * V1)
Replacing the given values we have:
T2 = 1.20 atm * 225 ml * 273.25 K / (1 atm * 246 ml)
T2 = 230 K
Answer: The final temperature is 230 K