Chemistry Data Test

chemical equilibrium

In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products do not change with time.

Conditions for chemical equilibrium

1. the system must be closed

2. equilibrium is dynamic process

3. the rates of the forward reaction and reverse must be equal

4. the amounts of reactants and products do not have to be equal ( after equilibrium is attained amounts will be constant)

Reversible Reactions

if activation energies in both directions can be overcome, then reversible reaction is possible (the products can revert to the original reactants)

static equilibrium

occurs when the reaction has stopped

dynamic equilibrium

occurs when the the forward and reverse rates of reaction are equal

disturbance

is any event which results in the equilibrium being affected

Le Chatelier's Principle

is stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress

shift in equilibrium: concentration

• ↑ concentration to either side, the opposite side will be favored

• ↓ concentration to either side, the same side will be favored

shift in equilibrium: pressure

• ↑ pressure, shift in direction to side with fewer moles (gas only)

• ↓ pressure, shift in direction to side with more moles (gas only)

shift in equilibrium: volume

• ↑ volume shift in direction to side with more moles (gas only)

• ↓ volume, shift in direction to side with fewer moles (gas only)

shift in equilibrium: temperature

• exothermic reaction → heat will be product (-h value)

• endothermic reaction → heat will be reactant (+ h value)

• ↑ heat to endothermic, shift right (favors products)

• ↑ heat to exothermic, shift to left (favors reactants)

• ↓ heat to endothermic, shift to left (favors reactants)

• ↓ heat to exothermic, shift right (favors products)

shift in equilibrium: catalysts

• presence of catalyst, both forward and reverse reactions rates increase equally

• catalysts do not affect the final equilibrium position

equilibrium constant (law of chemical equilibrium)

• used to determine if reaction at equilibrium favors reactants or products

• equilibrium constants of reverse reactions the reciprocal of the equilibrium constant forward reaction

• if Kc is more than 1 → formation products favored

• if Kc is less than 1 → formation reactants favored

equilibrium constant: change in temperature

• ↑ heat to endothermic, ↑ value of Kc

• ↑ heat to exothermic, ↓ value of Kc

• ↓ heat to endothermic, ↓ value of Kc

• ↓ heat to exothermic, ↑ value of Kc

Equilibrium graph (concentration)

One chemical has a spike (or dropped) and the others haven't changed

Equilibrium graph ( pressure/volume)

All chemicals spike in concentration (or drop)

Equilibrium graph (temperature)

either reactants or products spike or drop

Strong Acid

dissociates completely in water (H+)

strong base

dissociates completely in water ( OH-)

Monoprotic

an acid that can donate only one proton (H+ ion) per molecule (e.g., HCl)

Polypratic

an acid that can donate more than one proton per molecule

HClO4

perchloric acid, strong acid

HCl

hydrochloric acid, strong acid

HBr

hydrobromic acid, strong acid

HI

hydroiodic acid, strong acid

HNO3

nitric acid, strong acid

H2SO4

sulfuric acid, strong acid

LiOH

lithium hydroxide, strong base

NaOH

sodium hydroxide, strong base

KOH

potassium hydroxide, strong base

Ca(OH)2

calcium hydroxide, strong base

Sr(OH)2

strontium hydroxide, strong base

Ba(OH)2

barium hydroxide, strong base

Bronsted-Lowry acid

a substance that donates a proton to another substance

Bronsted-Lowry base

a substance that accepts a proton

conjugate acid

the particle formed when a base gains a hydrogen ion

conjugate base

the particle that remains when an acid has donated a hydrogen ion

Buffer

weak acid or base that can react with strong acids or bases to help prevent sharp, sudden changes in pH

pH

-log10 (H3O+ or H+)

pOH

-log[OH-]

Titrant

A solution of known concentration that is used to titrate a solution of unknown concentration

Titrand or Analyte

the solution whose concentration has to be determined

equivalence point

occurs when the moles of acid equal the moles of base in a solution ( only contains water and salt) sleepiest part of titration curve (middle of it)

end point

the point of color change of indicator ( shows the complete reaction has taken place)

mid point

located in the middle of the buffer zone halfway between equivalent point and the beginning point

Buffer region

The portion of a titration curve in which the concentration of an acid is approximately equal to that of its conjugate base; pH remains relatively constant through this region