Molarity, Molarity, and Percent Concentration

Example: What is the molarity of a solution prepared by dissolving 15.0 g of sodium hydroxide in enough water to make a total of 225 mL of solution?
Method 1:

• Calculate the number of moles of solute present.

  mol NaOH	=	30.0g NaOH	x	1 mol NaOH
  				80.0 g NaOH
  mol NaOH	=	0.750 mol NaOH

  
  
• Calculate the number of liters of solution present.

  L soln	=	500 mL	x	1 L	=	0.500 L soln
  				2000 mL

• Divide the number of moles of solute by the number of liters of solution.

  M	=	0.750 mol NaOH	=	1.67 M NaOH
  		0.500 L soln

le chatelier's principle

In 1884 the French chemist and engineer Henry-Louis Le Chatelier proposed one of the central concepts of chemical equilibria. Le Chatelier's principle can be stated as follows: A change in one of the variables that describe a system at equilibrium produces a shift in the position of the equilibrium that counteracts the effect of this change.
Le Chatelier's principle describes what happens to a system when something momentarily takes it away from equilibrium. Changing the concentration of one of the components of the reaction
 changing the pressure on the system

 changing the temperature at which the reaction is run.

Graham's Law Of Effusion

Graham's Law

Rates of diffusion and effusion depends on relative velocities of  gas molecules.  Diffusion is a natural tendency for mobile particles(gas and liquid) to travel continously and to go from areas  of high concentration to areas of low concentration by gradual mixing and virtue of their kinetic properties. 

Recall that average kinetic energy of molecules of any gas equals 1/2mv² and comparing two different gases:   1/2mv²=1/2mv²

As the mass of a gas increases, the velocity decreases and all gases will have the same average  kinetic energies at a given temperature.

Graham’s Law is written as:

Rate of diffusion of A   =         Molar Mass B

Rate of diffusion of B               Molar Mass A   


Graham’s law of effusion/diffusion  states that the rates of movement of gases at the same temperature and pressure are inversely proportional to the square roots of their molar masses.

Given a specific temperature and pressure, gases will move (diffuse or effuse) faster if their molar mass is low and slower if their molar mass is high.  This is true because their kinetic energy is the same but lighter gases need to travel at greater velocities.

Consider the fragrance industry.  Would we want our cologne or perfume to travel faster or slower.  A lady may get more attention the real purpose of fragrance if it travels faster.  However the fast traveling low mass fragrance would need to be applied more frequently.  This is among the many things to be considered as a chemist in this industry.

5 Postulates of KMT

1. A gas consists of a collection of small particles traveling in straight-line motion and obeying Newton's Laws.
2. The molecules in a gas occupy no volume (that is, they are points).
3. Collisions between molecules are perfectly elastic (that is, no energy is gained or lost during the collision).
4. There are no attractive or repulsive forces between the molecules.
5. The average kinetic energy of a molecule is 3kT/2. (T is the absolute temperature and k is the Boltzmann constant.)
6. Molecules of a gas have no attraction towards each other.
7. 7.