Final answer:
The new temperature of a gas that was initially at STP and then had its volume increased to 3.1L and pressure changed to 18psi is approximately 339.55 Kelvin, after converting the pressure from psi to atm and using the combined gas law to solve for the new temperature.
Step-by-step explanation:
Finding the New Temperature of a Gas after Volume and Pressure Change
When a container with a gas at Standard Temperature and Pressure (STP) changes in volume, with a different pressure, we can determine the new temperature using the combined gas law. Given that the original volume is 2.5L (at STP, where temperature is 273.15 K and pressure is 1 atm), and the new volume is 3.1L with a pressure of 18 psi (which equates to about 1.24 atm), we can find the new temperature after conversion.
First, we convert 18 psi to atmospheres since STP is defined using atmospheres:
18 psi * (1 atm / 14.696 psi) = 1.24 atm (approx.)
Now, using the combined gas law (P1V1/T1 = P2V2/T2), and knowing that T1 is 273.15 K, P1 is 1 atm, and V1 is 2.5L, we can solve for the new temperature T2:
(1 atm * 2.5L) / 273.15 K = (1.24 atm * 3.1L) / T2
T2 = (1.24 atm * 3.1L * 273.15 K) / (1 atm * 2.5L)
T2 ≈ 339.55 K
The new temperature of the gas after the increase in volume to 3.1L and change in pressure to 18 psi is approximately 339.55 Kelvin.