Module Six - Thermochemistry Flashcards
What is partial pressure?
Partial pressure is the pressure that one gas in a mixture of gasses would exert if it occupied the same volume by itself (at the same T and n).
What is Dalton’s Law of Partial Pressures?
The total pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases in the mixture.
How does Dalton’s law work?
It works because ideal gas molecules don’t sense each other - there are no attractions or repulsions.
What is Dalton’s Law equation?
P1 = (n1/ntotal) * Ptotal.
n1/ntotal is also abbreviated as X1.
A gas that makes up 21% of a mixture, or X=.21, will contribute 21% of total pressure.
An object’s kinetic energy depends on it’s _ and it’s _.
It’s speed an it’s mass - according to Ek = 1/2mv^2.
The speed of individual gas molecules change from time to time when…
They collide with an exchange energy with other molecules.
At any given time in a gas…
A few molecules are moving at high speed, most are at average speed, and some are colliding with the surface, so they momentarily have a speed of 0.
What is the kinetic-molecular theory?
A gas consists of tiny molecules in rapid, random, constant motion. There are four postulates of this theory.
What is the first postulate of kinetic-molecular theory?
A gas is composed of molecules whose size is much, much smaller than the distances between them. This accounts for the ease that gasses can be compressed, and the fact that gases at ordinary temp and pressure will mix with each other. These facts imply that there is a lot of unoccupied space in gasses.
What is the second postulate of the kinetic-molecular theory?
Gas molecules move randomly at various speeds and in every possible direction. This is consistent with the fact that gasses quickly and completely fill any container they are placed in.
What is the third postulate of the kinetic-molecular theory?
Except when gas molecules collide, forces of attraction and repulsion between them are negligible. Collisions with molecules in the walls of a solid container account for gas pressure. This accounts for the fact that all types of gasses behave the same way, despite the types of noncovalent interactions among their molecules.
What is the fourth postulate of the kinetic-molecular theory?
When collisions between molecules appear, the collisions are elastic. Elastic collisions are when the speeds of colliding molecules may change, but the total kinetic energy of two colliding molecules is the same after a collision as it is before a collision. This is consistent with the fact that a gas sample at a constant temperature never “runs out”with all of the molecules falling to the bottom of a container.
What is the fifth postulate of the kinetic-molecular theory?
The average kinetic energy of gas molecules is proportional to the absolute temperature. Though not part of the kinetic-molecular theory /really/, it is consistent with the fact that gas molecules can escape through a tiny hole faster if temperature increases.
At a given temperature, the kinetic energy of the molecules of one gas is…
the same as for any other gas. For this to be possible, the larger m is the smaller the average v must be.
At the same temperature, heavier gas molecules have _ average speed than lighter ones.
slower average speed.
What is the equation for the kinetic energy of one molecule?
KE=1/2mv^2, where v is speed, or m/s, of one particle.
