To determine the initial pressure of the gas, we can use the combined gas law, which relates the initial and final conditions of a gas sample:
(P1 * V1) / (T1) = (P2 * V2) / (T2)
Where: P1 = Initial pressure of the gas V1 = Initial volume of the gas (1.5 L) T1 = Initial temperature of the gas (38 °C + 273.15 K) P2 = Final pressure of the gas (STP pressure = 1 atmosphere) V2 = Final volume of the gas (2.35 L) T2 = Final temperature of the gas (STP temperature = 273.15 K)
Converting the initial temperature from Celsius to Kelvin: T1 = 38 °C + 273.15 K = 311.15 K
Plugging in the values into the equation:
(P1 * 1.5 L) / (311.15 K) = (1 atm * 2.35 L) / (273.15 K)
Simplifying the equation:
P1 = (1 atm * 2.35 L * 311.15 K) / (1.5 L * 273.15 K)
P1 ≈ 1.699 atm
Therefore, the initial pressure of the gas is approximately 1.699 atmospheres.