Basic Concepts
What does 'partial pressure' mean?
The pressure that each individual gas would create if it was alone in the container
If P₁ = 30 kPa and P₂ = 70 kPa, what is P_total?
100 kPa (just add them: 30 + 70 = 100)
Name ONE place where Dalton's Law is used in real life.
SCUBA diving, aviation, medicine, space exploration, or weather balloons (any one is correct!)
Write Dalton's Law formula.
P_total = P₁ + P₂ + P₃ + ...
In air, which gas has the highest partial pressure?
Nitrogen (N₂) - it makes up 78% of air!
Air is 21% oxygen. If total pressure is 100 kPa, what is oxygen's partial pressure?
21 kPa (100 × 0.21 = 21)
Why do SCUBA divers need to know about partial pressures?
To calculate safe breathing gas mixtures at different depths underwater
Write the partial pressure formula using mole fraction.
P_A = X_A × P_total
True or False: In a gas mixture, each gas acts independently of the others.
TRUE! That's the whole point of Dalton's Law!
A mixture has 3 moles He and 7 moles Ne. What is the mole fraction of helium?
X_He = 3/(3+7) = 3/10 = 0.3
What gas keeps you alive but can be toxic at high partial pressures?
Oxygen (O₂)! Too much oxygen pressure can cause oxygen toxicity
Write the mole fraction formula.
X_A = (moles of gas A) / (total moles)
What creates gas pressure in a container?
Gas molecules hitting (colliding with) the walls of the container
If X_A = 0.4 and P_total = 250 kPa, find P_A.
P_A = 0.4 × 250 = 100 kPa
At high altitudes, why is it harder to breathe?
Lower total air pressure means lower partial pressure of oxygen, so less O₂ enters your lungs
Bonus point
+400
If you remove one gas from a mixture, what happens to the total pressure?
The total pressure DECREASES by the amount of that gas's partial pressure
A tank has O₂ (40 kPa), N₂ (120 kPa), and Ar (15 kPa). What's the total pressure?
175 kPa (40 + 120 + 15 = 175)
Astronauts breathe pure oxygen at 1/5 normal pressure. Why does this work?
The partial pressure of oxygen stays the same (0.21 atm), so they get enough oxygen even though total pressure is lower!