Gas Laws

4. EVALUATE
• Are the units correct? Yes; units canceled to give mL of H2. • Is the number of significant Yes; the number of significant figfigures
correct? ures is correct because data were
given to three significant figures.
• Is the answer reasonable? Yes; the temperature increases, and
the pressure decreases, both of
which have the effect of making the
volume larger.
PRACTICE
In each of the following problems, it is assumed that the molar quantity
of gas does not change.
1. Calculate the unknown quantity in each of the following measurements
of gases.
P 1 V 1 T 1 P 2 V 2 T 2
a. 99.3 225 mL 15°C 102.8 ? mL 24°C
kPa kPa
b. 0.959
atm
3.50 L 45°C ? atm 3.70 L 37°C
c. 0.0036 62 mL 373 K 0.0029 64 mL ? K
atm atm
d. 100. 43.2 mL 19°C 101.3 ? mL 0°C
kPa kPa
2. A student collects 450. mL of HCl(g) hydrogen chloride
gas at a pressure of 100. kPa and a temperature
of 17°C. What is the volume of the HCl at 0°C and
101.3 kPa? ans: 418 mL
DALTON’S LAW OF PARTIAL PRESSURES
ans: 224 mL
ans: 0.884 atm
ans: 310 K
ans: 39.9 mL
Air is a mixture of approximately 78% N2, 20% O2, 1% Ar, and 1%
other gases by volume, so at any barometric pressure 78% of that pressure
is exerted by nitrogen, 20% by oxygen, and so on. This phenomenon
is described by Dalton’s law of partial pressures, which says that the total
pressure of a mixture of gases is equal to the sum of the partial pressures
of the component gases. It can be stated mathematically as follows.
PTotal PGas 1 PGas 2 PGas 3 PGas 4 …
Gas Laws 129