Applications of the Gas Laws (5.2.3) Flashcards
• When determining the number of moles of gas collected over water, the partial pressure of water vapor in the gas sample must be taken into account.
• When determining the number of moles of gas collected over water, the partial pressure of water vapor in the gas sample must be taken into account.
• Helium balloons and hot air balloons float because the gas contained within them has a lower density than the atmosphere.
• Helium balloons and hot air balloons float because the gas contained within them has a lower density than the atmosphere.
Collecting a gas over water is a technique that
allows gas produced from a reaction to be collected
without mixing it with air.
When determining the number of moles of gas
collected over water, the partial pressure of water
vapor in the gas sample must be taken into account.
Mg(s) + 2HCl(aq) ! MgCl2(aq) + H2(g)
Mg metal is reacted with HCl and the gas produced
is collected over water. If 36.0 mL of gas are
collected at 20.0˚C and 765.0 torr total pressure,
how many moles of H2 are formed? The vapor
pressure of water at 20˚C is 17.5 torr.
First, use Dalton’s law of partial pressures to
calculate the partial pressure of H2.
Next, use the ideal gas law (PV = nRT) to calculate
moles of H2. The pressure must be converted to
atmospheres and the temperature to kelvins.
Solving for n yields 1.47 x 10–3 mol H2.
Why do helium balloons float at room temperature?
Less dense substances float over more dense
substances.
1.00 mol of any gas occupies 24.4 L at 1.00 atm
and 298 K (room temperature).
However, 1.00 mol He weighs 4.00 g, while
1.00 mol N2 (the major component of air) weighs
28.0 g.
The density of helium is lower than the density of
nitrogen, so helium balloons float.
Collecting a gas over water is a technique that
allows gas produced from a reaction to be collected
without mixing it with air.
When determining the number of moles of gas
collected over water, the partial pressure of water
vapor in the gas sample must be taken into account.
Mg(s) + 2HCl(aq) ! MgCl2(aq) + H2(g)
Mg metal is reacted with HCl and the gas produced
is collected over water. If 36.0 mL of gas are
collected at 20.0˚C and 765.0 torr total pressure,
how many moles of H2 are formed? The vapor
pressure of water at 20˚C is 17.5 torr.
First, use Dalton’s law of partial pressures to
calculate the partial pressure of H2.
Next, use the ideal gas law (PV = nRT) to calculate
moles of H2. The pressure must be converted to
atmospheres and the temperature to kelvins.
Solving for n yields 1.47 x 10–3 mol H2.
Why do helium balloons float at room temperature?
Less dense substances float over more dense
substances.
1.00 mol of any gas occupies 24.4 L at 1.00 atm
and 298 K (room temperature).
However, 1.00 mol He weighs 4.00 g, while
1.00 mol N2 (the major component of air) weighs
28.0 g.
The density of helium is lower than the density of
nitrogen, so helium balloons float.
How do hot air balloons work? 1.00 mol of gas at 1.00 atm and 600 K occupies 49.2 L, while 1.00 mol of gas at 1.00 atm and 298 K occupies 24.4 L. This means that the density of hot air inside a balloon (0.569 g/L) is lower than the density of the surrounding air (1.15 g/L). This causes hot air balloons to float.
How do hot air balloons work? 1.00 mol of gas at 1.00 atm and 600 K occupies 49.2 L, while 1.00 mol of gas at 1.00 atm and 298 K occupies 24.4 L. This means that the density of hot air inside a balloon (0.569 g/L) is lower than the density of the surrounding air (1.15 g/L). This causes hot air balloons to float.
