Gases Daltons Law of Partial Pressures Partial Pressure

Gases Dalton’s Law of Partial Pressures

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

Partial Pressures

Example 1 47 L He and 12 L O 2 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.

Example 1 Ø Find moles of each gas:

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

Partial Pressure shows that the identities of the gases do not matter, just the number of moles Ø so, for ideal gases: Ø 1. 2. Ø size of gas molecule is not important forces between molecules is not important these are things that would change with the identity of the gas

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

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

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 0. 650 L and the vapor pressure of water at 22°C is 21 torr. Calculate the partial pressure of O 2 in the gas collected and the mass of KCl. O 3 that was decomposed.

Example 2 Ø Find the partial pressure of O 2 Ø Find the number of moles of O 2

Example 2 Ø Find the moles of KCl. O 3 needed: Ø Find the grams of KCl. O 3 needed:

Gases Kinetic Molecular Theory

The Kinetic Molecular Theory Ø model of gas behavior so only an approximation volume of particles is assumed to be zero 2. particles are in constant motion 3. particles exert no forces on each other (no attraction or repulsion) 4. kinetic energy is proportional to Kelvin temperature 1.

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

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

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

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

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

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

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

Velocity of Particles As the temperature increases: Ø the average velocity increases Øthe spread of velocities increases

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