6.78 a two-phase liquid–vapor mixture of refrigerant 134a is held in a large storage tank at 100 lbf/in.2, 50°f, as illustrated in fig. p6.78. a technician fills a 3.5-ft3 cylinder that is initially evacuated to take on a service call. the technician opens a valve and lets refrigerant from the storage tank flow into the cylinder until the pressure gage on the cylinder reads 25.5 lbf/in.2 (gage). the surrounding atmospheric pressure is 14.5 lbf/in.2 assuming no heat transfer and neglecting kinetic and potential energy effects, determine the final mass of refrigerant in the cylinder, in lb, and the amount of entropy produced, in btu/°r.

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.

the answer is 1260

you spend 7 hours in school for 1 school day with 5 school days in 1 school week with 36 school weeks in a school year.

7*5*36= 1260 it's all about multiplying