Aptitude Test Problems in Physics Science for Everyone by S Krotov ( PDFDrive.com )

228 Aptitude Test Problems in Physics

problem, we obtain the initial and final tempera-

tures in the vessel:

pi = 17 x 10 5 Pa, T 1 = Ti cy_- 380 K, ,

pt = 26 X 10 5 Pa, T2 = T1 CI-j 440 K.

Let us now determine the mass of evaporated
water. Assuming that water vapour is an ideal gas,
we calculate the initial pvi and final Pv2 pressures
of water vapour in the vessel. For this purpose,
we make use of the obtained graphs. For T 1 =
380 K, the pressure of hydrogen is pii2 15.5 X
105 Pa, and

Pv = PI —Pi", 1.5X10^5 Pa.

For T2 = 440 K, ph 2 c•- 18 x 10 5 Pa, and

Pv2--= Pf- 13 1-1 ' 8 x10^5 Pa.

Let us write the equations of state for water

vapour at pv„, T 1 and pv 2, T2:

PviV = m v 1

ltv

R T 1 , Pv2r = — mv2 RT 2 ,

where mv, and mv2 are the initial and final masses

of vapour in the vessel. Hence we can determine

the mass of evaporated water:

Pv2 Pvi

Am =-mv- (^2) — my). =
R k T 2 Ti
18 x 10-3 kg/mol X 2 x 10 -3m 3
8.3 JAK • mol)
( 440 K 380 K
8 Pa 1.5 Pa )
X X 10 5 = 6 x 10-3 kg= 6 g.
2.23. If h is the height of water column in the
capillary, the temperature of the capillary, and
hence of water at this height, is
Th=
Tu ph