CONCEPTUAL/SITUATIONAL
Situation: A sealed syringe is partially
filled with air. If you push the plunger down
without opening the tip, what happens to
the pressure inside? What happens if you
pull the plunger outward instead? Explain
using gas laws.
Explanation: When you push the plunger
down, the volume of air inside the syringe
decreases, causing the pressure to
increase (Boyle’s Law: P₁V₁ = P₂V₂). This is
because gas molecules have less space to
move, leading to more frequent collisions.
On the other hand, pulling the plunger
outward increases the volume, which
decreases the pressure inside the syringe.
This creates a partial vacuum, which is
why liquids can be drawn into the syringe
when the tip is placed in a fluid.
Situation: A diver exhales a bubble of air
while 20 meters underwater. As the bubble
rises to the surface, what happens to its
size? Explain using gas laws.
Explanation: As the bubble rises, the
external water pressure decreases.
According to Boyle’s Law (P₁V₁ = P₂V₂),
when pressure decreases, volume
increases. This means the bubble will
expand as it gets closer to the surface. This
is why divers must exhale when ascending
to prevent lung overexpansion due to
expanding gases in their lungs.
Situation: A sealed, empty plastic bottle is
placed in the freezer overnight. The next
morning, the bottle appears slightly
crushed. What caused this change in
shape?
Explanation: According to Charles’s Law
(V₁/T₁ = V₂/T₂), when the temperature of a
gas decreases, its volume also decreases
if the pressure is constant. As the air inside
the bottle cools down, it contracts,
creating lower pressure inside compared
to the external atmosphere. This
difference in pressure causes the bottle to
collapse slightly.
Situation: A car tire is properly inflated on
a hot summer afternoon. However, when
checked the next morning when the
temperature is much lower, the tire
appears underinflated. What happened?
Explanation: According to Charles’s Law
(V₁/T₁ = V₂/T₂), when temperature
decreases, the volume of the gas inside
the tire also decreases if pressure remains
constant. Since the air molecules inside
the tire move slower in cold temperatures,
they take up less space, making the tire
appear underinflated.
Situation: A metal container with a small
opening is placed in direct sunlight for
hours. Suddenly, a hissing sound is heard
from the opening. What caused this?
Explanation: According to Gay-Lussac’s
Law (P₁/T₁ = P₂/T₂), when temperature
increases, the pressure of a gas also
increases if volume is constant. As the air
inside the container heats up, its pressure
rises. Eventually, when the pressure
becomes too high, some of the gas
escapes through the opening, causing the
hissing sound.
Situation: A warning label on an aerosol
can states, "Do not incinerate." Explain
why this warning is important from a gas
law perspective. What happens to the gas
inside the can when it's heated, and why is
this dangerous?
Explanation: When you heat an aerosol
can, the gas inside gets hotter. According
to Gay-Lussac's Law, when the
temperature goes up and the volume stays
the same, the pressure inside the can also
increases. If the pressure gets too high, the
can might burst or even explode. This is
why it's dangerous to heat or burn aerosol
cans—they could easily rupture because
the pressure inside becomes too much for
the can to handle.
Situation: A basketball is pumped to its
ideal pressure indoors at 25°C. Later, the
ball is taken outside to a colder
environment at 5°C. Will the ball feel
softer, harder, or stay the same? Explain.
Explanation: According to the Combined
Gas Law (P₁V₁/T₁ = P₂V₂/T₂), if
temperature decreases while volume
remains constant, the pressure of the gas
inside the basketball also decreases.
Since the air molecules move slower at
lower temperatures, they exert less force
on the inner walls of the ball, making it feel
softer.
Situation: A sealed gas tank is transported
from sea level to a high-altitude location.
The temperature remains the same, but
the external atmospheric pressure is lower
at higher altitudes. What will happen to the
gas inside the tank?
Explanation: The gas inside the tank
remains at the same temperature and
volume, but since the external pressure
decreases at high altitudes, the pressure
difference between the inside and outside
increases. This could make the tank
expand slightly or even risk bursting if it is
not built to withstand the pressure
difference. This is why pressurized
containers have safety valves to release
excess pressure.
Situation: Two identical balloons are filled
with different gases—one with oxygen and
the other with nitrogen. If both have the
same number of molecules and are at the
same temperature and pressure, which
balloon will be larger?
Explanation: According to Avogadro’s
Law, at constant temperature and
pressure, equal amounts of gas (same
number of moles) will occupy equal
volumes, regardless of the gas type. Since
both balloons have the same number of
molecules, they will have the same
volume.
Situation: A sealed soda bottle is taken
from a refrigerator (4°C) and left in direct
sunlight (35°C). If the bottle does not
expand, what will happen to the pressure
inside?
Explanation: According to the Combined
Gas Law (P₁V₁/T₁ = P₂V₂/T₂), if volume
remains constant and temperature
increases, the pressure inside must also
increase. The gas molecules inside the
bottle will move faster, colliding more
frequently with the bottle walls, leading to
an increase in pressure. This is why soda
bottles sometimes burst when exposed to
heat.
Situation: A scientist needs to fill a
weather balloon so that it will expand to a
specific size when it reaches high
altitudes. Should the balloon be
completely filled at ground level or
partially filled? Why?
Explanation: The balloon should be
partially filled at ground level. According
to the Ideal Gas Law, as the balloon
ascends, the external pressure decreases.
Since the balloon is flexible, the gas inside
will expand, increasing the volume. If it is
completely filled at ground level, it might
burst when it reaches high altitudes due to
the expanding gas.
Question: Why is it important to use
absolute units in gas laws?
Explanation: We use absolute units in gas
laws to keep things accurate and
consistent. For pressure, we use pascals,
for volume, we use liters or cubic meters,
and for temperature, we use kelvins.
Kelvins are important because they start at
absolute zero, so we don’t end up with
negative values that could mess up the
calculations.