CHEMISTRY UNIT TEST #4

Equilibrium

When the rate of the forward reaction is equal to the rate of the reverse reaction

What happens at equilibrium

concentrations of reactants and products will remain constant

what sort of system can equilibrium occur in

closed system

homogenous equilibrium

reactants and products in the same phase

heterogenous equilibrium

reactants and products are in different phases

le chatelier's principle

When a chemical system at equilibrium is disturbed by a stress, the system adjusts (shifts) to oppose the change

stresses in a system

change in concentration
change in pressure (or volume)
change in temperature

chemical equilibrium

equilibrium between reactants and products of a chemical reaction

phase (or physical) equilibrium

equilibrium between different physical states of a pure substance

Large Keq value (Keq>> 1)

the reaction produces more product

Small Keq value (Keq<< 1)

the reaction produces more reactant

Keq = 1 (or very close to 1)

the reaction produces an equal amount of reactant & product

increasing the concentration of reactants or decreasing the concentration of products

will favour the forward reaction, and will shift towards the right

decreasing the concentration of the reactants or increasing the concentration of the products

will favour the reverse reaction, and will shift towards the left

increasing the volume of the container/decreasing the pressure

cause a shift towards the reaction towards the side with more gas molecules

descreasing the volume of the container or increasing the pressure

will cause a shift to the side with less gas molecules

in an exothermic reaction, increasing the temperature

system will shift to the left

in an exothermic reaction, decreasing the temperature

system will shift to the right

in an endothermic reaction, increasing the temperature

will cause a shift to the right

in an endothermic reaction, decreasing the temperature

will cause a shift to the left

variables that do not affect equilibrium

catalysts, inert gases

catalysts

increase reaction rate, lower activation energy of both forward and reverse.

inert gases

increases the pressure, will increase reaction rate, increases the probality of successful collisions for both products and reactants equally

ICE TABLES

i: initial concentration (mol/L)
c: change in concentration
e: equilibrium concentration (mol/L)

+x

if increasing in concentration

-x

if decreasing in concentration

change in concentration

change in concentration is always negative for reactants and positive for products

equilibrium position

the relative concentrations of reactants and products in a system in dynamic equilibrium

reversible reaction

a chemical reaction that proceeds in both the forward and reverse directions, setting up an equilibrium in a closed system

equilibrium law

the mathematical description of a chemical system at equilibrium

properties of acids

* they are corrosive
* they taste sour
* pH < 7
* Turn Bromothymol ^^blue^^ $yellow$
* turn ==red== litmus paper ^^blue^^
* turns fuschia

properties of bases

* they are corrosive
* they taste bitter
* turn bromothymol ^^blue^^ the colour ^^blue^^
* turn ^^blue^^ litmus paper ==red==
* stays clear

bronsted-lowry theory

a theory that states an acid is a hydrogen atom donour, whereas a base is a hydrogen ion acceptor

arrhenius theory

a theory that states that in aqueous solutions, acids are substances that produce hydrogen ions, whereas bases produce hydroxide ions

hydronium ions

a water molecule that has accepted a hydrogen ion, H3O+

conjugate acids

the substance that forms when a base, according to the bronsted-lowry theory accepts a hydrogen ion

conjugate base

the substance that forms when an acid according to the bronsted-lowry theory donates a hydrogen ion

conjugate base pair

two substances that act as a Bronsted-Lowry acid and base that are related by the gain or loss of a proton

strong acids

an acid that completely ionizes in water, producing hydrogen ions

weak acids

an acid that only partly ionizes in water, producing hydrogen ions

magnitude of Ka for strong acids

Ka> 1

magnitude of Ka for weak acids

ka

pH of an acid with a high concentration

low pH

pH of an acid with a low concentration

high pH

acid with low pH

high Ka value

acid with high pH

low Ka value

weak base

a base that only partly reacts with water to produce hydroxide ions

strong base

a base that dissociates completely in water to produce hydroxide ions

ka expression

ka is the equilibirum constant for the ionization of an acid, also called acid dissociation constant

kb expression

the equlibrium constant for the ionization of a base, also called base dissociation constant

autoionization of water

the transfer of a hydrogen ion from one water molecule to another

amphiprotic

the ability to donate/accpet a hydrogen ion and act as both an acid and base

kw expression

the equlibrium constant for the autonization of water

pH

the negative logarithm of the concentration of hydrogen ions in an aqueous solution

pOH

the negative logarithm of the concentration of hydroxide ions in an aqueous solution

monoprotic acid

an acid that possesses only one ionizable hydrogen atom

polyprotic acid

an acid that possesses more than one ionizable hydrogen atom

percent ionization

percent ionization is used to express how much a weak acid or base ionizes