Chemistry 101 or How to understand chemistry . Part IV

Equilibrium Le Chatelier's Principle

Any chemical reaction go both way

According to Le Chatelier, the position of equilibrium will move to counteract the change.
If reaction produces heat then heating the system will move equilibrium to the left
And cooling the system will move equilibrium to the right. If volume of the products is
greater than volume of the reactants then increasing the pressure will move equilibrium to the left. Decreasing pressure will move equilibrium to the right. Increasing concentration of reactants will move equilibrium to the right, increasing concentration of the products will move equilibrium to the left.

Equilibrium constant Keq = [C] * [D] / [A] * [B] where [ ] is concentration in Moles

2H₂S <=> 2H₂ + S₂ concentration of products and reactants is raised to the power of their respective coefficients.

Keq = [H2]² * [S2] / [H2S]²

pH Acidity or Basicity of a solution.

PH = -Log [H+] where [H+] is concentration of H+ ions.

What is log? log is logarithm with base 10. Log 10 = 1 because 10¹ = 10

Log100 = 2 because 10² = 100.     Log 1000 = 3 because 10³ = 1000

log1/1000 = -3 because 10^-3 = 1/1000

- log 1/1000 = 3.

pH of water is 7 (neutral)

What is pH of 0.0001 N HCl?

HCl     =     H+     +      Cl-

Concentration of H+ equals concentration of HCl = 0.0001 N

pH = - log [1 * 10^-4] = 4

Liquid Properties

Freezing point constant = degree C per 1M of solute per 1000g of solvent.

For water Fpk = 1.86

Given: 1 M of NaCl solution. What is freezing point?

Pt = Molarity * Fpk = 1 * 1.86 = 1.86 C
Freezing point of water is 0 C then freezing point of solution = 0 C - 1.86 C = -1.86 C

Given: 196 g of H₂SO₄ added to 500 g of water. What is freezing point of the solution?

How many mole of H₂SO₄ is in 196g? MW = 2+32+64=98g

196g/98g = 2 M.     is in      500g
                    X M     is in      1000g     X = 2 * 1000 / 500 = 4 M

Fr p. depression =4 M * 1.86 C = 7.44 C

Frp = 0 C - 7.44C = -7.44 C Where 0C Freezing point of water.

Boiling Point

Boiling point depends on number of solute particles per number of solvent particles.

For water Kb = 0.52

Given: 106 g Na₂CO₃ in 500 g of water. What is boiling point of the solution?

MW of Na₂CO₃= 23+23+12+48 = 106

106 g      in     500 g water
Xg      in     1000g water X = 106 * 1000 / 500 = 212 g

106 g/L      -      1 M
212 g/L      -      X M     X = 212 / 106 = 2 M.

Bp. raise = 2 M * 0.52 = 1.4 C Bp = 100 C + 1.4 C = 101.4 C

Buy CHEMISTRY FOR STUDENTS AND PARENTS from Amazon

My chemistry tutorial is focused on key chemistry topics: Oxides, Bases, Acids, Salts, Equivalent proportions, Acid Base reactions, Weigh and Volume problems, Equilibrium, Le Chatelier's Principle, Liquid Properties: Freezing and Boiling points, Balance Redox Reactions (30 examples with explanations), Stoichiometry (30 problems with answers and solutions). Study my tutorial and you will understand chemistry.

Part III

Sign in for Chemistry Quiz