A flask with a volume of 1.50 L, provided with a stop-cock, contains ethane gas (C2H6) at 300 K and atmospheric pressure (1.013 X 105 Pa). The molar mass of ethane is 30.1 g/mol. The system is warmed to a temperature of 550 K, with the stopcock open to the atmosphere. The stopcock is then closed, and the flask is cooled to its original temperature. (a) What is the final pressure of the ethane in the flask? (b) How many grams of ethane remain in the flask?
Solution 62P Step 1: We can use here the equation, P V = n RT 1 1 1 1 Where R = 8.315 (for C H ) 2 6 P1V 1 1.013×10 ×1.5×103 n =1 RT1 = 8.315×300 = 0.0609 mol The number of moles in the hot gas is, P1V 1 1.013×10 ×1.5×103 n =2 RT 2 = 8.315×550 = 0.0032 mol