LQ_Gases 1 Solutions Marks (a) Any three of the following: All molecules are identical and have the same mass. All molecules are moving randomly. Size of molecules is negligible. Duration of collision is negligible compared with the time between collisions. 3 1A All collisions are elastic. Intermolecular forces are negligible. (b) N is the number of molecules in the gas. m is the mass of a gas molecule. 1A 1A 2 c is the mean-square speed of the gas molecules. 1A (c) (i) Since 2 3 1 c Nm pV , and by pV = nRT , we have 2 3 1 c Nm = nRT 1A 2 c = Nm nRT 3 = A mN RT 3 1A (ii) 2 c = A mN RT 3 2 c = A mN RT 3 m 1 1M Carbon dioxide has the smallest root-mean-square speed as it has the largest mass. 1A (iii) From (ii), 2 2 N O c c = O N m m 1M 2 N c = 2 O N O c m m = 480 28 32 = 513 m s –1 1A The root-mean-square speed is 513 m s –1 . 1
LQ_Gases 2 Solutions Marks (a) (i) When energy is supplied to the gas, the average kinetic energy of the gas molecules increases. Since temperature is directly proportional to the average kinetic energy of the gas molecules, temperature also increases. 1A 1A (ii) By KE = nRT 2 3 , 1M KE = T nR 2 3 T = KE nR 3 2 = 120 31 . 8 2 3 2 = 4.81 K 1A The temperature increases for 4.81 K. (b) (i) By pV = nRT , Since the gases have the same volume and temperature, their pressure is also the same.
You've reached the end of your free preview.
Want to read all 7 pages?