Page 190 - Chemistry ICSE Class IX

178 ICSE Chemistry – 9

What are standard temperature and pressure (STP)
conditions
The following values of temperature and pressure are accepted as standard
temperature and pressure conditions:
ƒ Standard temperature = 273 K (or 0°C)
5
–2
5
ƒ Standard pressure = 1 bar = 10 N m = 10 Pa
What are the normal temperature and pressure (NTP)
conditions

The following values of temperature and pressure are accepted as the
normal temperature and pressure (NTP) conditions:
ƒ Normal temperature = 0°C or 273 K

ƒ Normal pressure = 1 atm
ƒ = 76 cm Hg
= 760 mm Hg
= 760 torr
Torr is the unit of pressure.
1 torr = 1 mm Hg column
Although the standard temperature and pressure (STP) and normal
temperature and pressure (NTP) are taken to be the same, but the two are
conceptually different. The difference between the STP and NTP values
is very small, and therefore for numerical point of view, either of the two
could be used.

EXAMPLE 7.8. Calculate the volume of one mole of oxygen at 27°C and
4 atmosphere pressure. The molar volume of oxygen at NTP is 22.4 L.
Solution: The NTP conditions correspond to 1 atm pressure and 273.15 K. Thus,
V = 22.4 L
1
V = ?
2
T = 273.15 K
1
T = (27 + 273.15) K = 300.15 K
2
P = 1 atm
1
P = 4 atm
2
P V P V
From gas equation, 1 1 = 2 2
T 1 T 2
P V T
V = 1 1 2
2
T P 2
1
Substituting the values, one gets
1 atm × 22.4 L × 300.15 K
V =
2
273.15 K × 4 atm
1 × 22.4 × 300.15
=
273.15 × 4
L = 6.15 L

Thus, one mole of oxygen at 27°C and 4 atm pressure would occupy a volume
of 6.15 L.