1. Dalton’s Law of Partial Pressures
Gases
Dalton’s Law of Partial Pressures

2. Partial Pressure
for a mixture of gases, the total pressure is the sum of the pressures each gas would exert if it were alone
using the ideal gas law, can change to:

3. Partial Pressures

4. Example 1
47 L He and 12 L O2 at 25°C and 1.0 atm were pumped into a tank with a volume of 5.0 L. Calculate the partial pressure of each gas and the total pressure in the tank.

5. Example 1
Find moles of each gas:

6. Example 1 Find the new P of each gas:
Find the total pressure of the gases:

7. Partial Pressure
shows that the identities of the gases do not matter, just the number of moles
so, for ideal gases:
size of gas molecule is not important
forces between molecules is not important
these are the things that would change with the identity of the gas

8. Mole Fraction
Mole Fraction: ratio of number of moles of a certain component of a mixture to number of moles total in mixture

9. Water Displacement
when gas is collected using water displacement, there is always a mixtures of gases
the pressure of water vapor varies with temperature and will be given in a problem

10. Example 2
The oxygen produced by the reaction below was collected by gas displacement at 22°C at a total pressure of 754 torr. The volume of gas collected was L and the vapor pressure of water at 22°C is 21 torr. Calculate the partial pressure of O2 in the gas collected and the mass of KClO3 that was decomposed.

12. Example 2 Find the partial pressure of O2
Find the number of moles of O2

13. Example 2 Find the moles of KClO3 needed:
Find the grams of KClO3 needed:

14. Kinetic Molecular Theory
Gases
Kinetic Molecular Theory

15. The Kinetic Molecular Theory
model of gas behavior so only an approximation
volume of particles is assumed to be zero
particles are in constant motion
particles exert no forces on each other (no attraction or repulsion)
kinetic energy is proportional to Kelvin temperature

16. Boyle’s Law: P and V
decrease in volume means that particles will hit wall more often and that will cause P increase

17. Gay-Lussac’s Law: P and T
the speed of particles increases as T increases so they hit the wall more often and with greater force and P increases

18. Charles’ Law: V and T
increase in T causes and increase in particle speed so they hit the wall more often
to keep P constant, the V must increase

19. Avogadro’s’ Law: V and n
increase in number of gas molecules would cause increase in P if V were held constant
to keep P constant, V must increase

20. Dalton’s Law
Kinetic Molecular Theory assumes that all particles are independent of each other

21. Temperature
Kelvin temperature is a sign of the random motions of gas particles
higher T means greater motion

22. Root Mean Square Velocity
Average Kinetic Energy
urms: the square root of the average of the squares of the particle velocities
Avogadro’s #
mass of particle
Must be in kg/mol

23. Velocity of Particles As the temperature increases:
the average velocity increases
the spread of velocities increases

24. Example 3
Calculate the root mean square velocity for the atoms in a sample of helium gas at 25°C.