Equilibrium

Question 1

once the products form, both the forward and reverse reactions will occur.

Answer 1

ultimately reaction will come to equilibrium: which both the forward and the reverse reactions occur at the same constant rate.
at equilibrium, overall concentration of the reactants and products remains the same.

Question 2

when the reaction is at equilibrium

Answer 2

the rate of the forward reaction = rate of reverse reaction

equilibria occur at closed systems ( no new products, reactants or other changes are imposed)

Question 3

the equilibrium constant

Answer 3

Keq= products/reactants at equilibrium

Question 4

the coefficient of each species (products and reactants) will become an exponent on its concentration in the equilibrium expression

Answer 4

solids and pure liquids are not included bc their concentrations don’t change.
if the reaction is gases, we can use the partial pressure of each gas as its concentration. constant using partial pressures is Kp

Question 5

Keq value is ___ at given temp

Answer 5

constant !

if the temp changes then the Keq will change

Question 6

the value of the Keq tells you the direction the reaction favours

Answer 6

if Keq<1 : reaction favour the reactants ( more reactants then products @ equalibrium)
if Keq=1 reaction has equal amounts of reactants and products
if Keq >1 : reaction favours the products, there are more products than reactants at equilibrium

Question 7

what is chemical equilibrium

Answer 7

its a dynamic equilibrium! : means that molecules are still reacting but there is no net change in the composition of the system.

Question 8

what is the reaction quotient?

Answer 8

if the reaction is not at equilibrium: then we use the reaction quotient Q

• in this the concentrations in the expression Q do not have to be the concentrations at equilibrium! whereas in Keq they did !
• if the concentrations are the equilibrium concentrations then Q= Keq

Question 9

what happens when you compare Q to Keq?

Answer 9

tells us what direction the reaction will proceed. the reaction will strive to reach a state in which Q= Keq.
if Q Keq: reaction will go in reverse direction in order to increase the concentration of the reactants and decrease the concentration of the products to reduce Q to Keq

Question 10

Le chatiliers principle

Answer 10

a system at equilibrium will try to neutralize any impose change in order to re-establish equilibrium!

Question 11

change in volume

Answer 11

if you decrease volume, pressure will inc and vice versa.

Question 12

changing the temp of a reaction mixture

Answer 12

exothermic reaction will release heat ( so we note on the product side) and then the H will be negative !
endothermic reaction consume heat that we will note on the left side of the equation like a reactant and H will be positive.
unlike changes in concentration or pressure, changes in temp will affect the Keq value.
heating a reaction will get it to equilibrium faster, but once its there adding or taking away heat will affect equilibrium predicted by le chatiliers prinicple.

Question 13

adding an inert or non reactive gas

Answer 13

it won’t participate in the reaction , so the partial pressure wont change and the concentration of the products and reactants won’t change. therefore no change in equilibrium.
however, if we inject an inert gas into a constant pressure container, the volume will change. ( it will increase).

Question 14

adding a catalyst

Answer 14

adding a catalyst to a reaction that’s already at equilibrium has no effect.
catalyst affects the reaction rate but does not affect the equilibrium.

Question 15

solution

Answer 15

a solution forms when one substance dissolve into another , forming a homogenous mixture

Question 16

solutions can involve any of the three phases of matter

Answer 16

gas in liquid
solid in liquid
solid in a solid etc

Question 17

when a solution has water as the solvent its called an ?

Answer 17

aqueous solution

Question 18

like dissolves like

Answer 18

solutes will dissolve best in solvents where intermolecular forces being broken in the solute are being replaced by equal or stronger intermolecular forces between the solvent and the solute.

Question 19

when ionic substances dissolve they dissociate into ?

Answer 19

ions! free ions in a solution are called electrolytes bc the solution can conduct electricity.
some salts dissociate completely into individual ions while others only partially dissociate.

Question 20

solutes that dissociate completely like ionic substances are called ?

Answer 20

strong electrolytes

solutions of strong electrolytes are better conductors of electricity than those of weak electrolytes

Question 21

those that remain ion paired to extent are called ?

Answer 21

weak electrolytes

Question 22

different ionic compounds will dissociate into diff number of particles. some won’t dissociate at all and others will break up into several ions

Answer 22

the van Hoff (ionizability factor) (i) tells us how many ions one unit of a substance will produce in solution.
ex) NaCl: i=2
CaCl2 : I=3

Question 23

what is the concentration?

Answer 23

concentration of a solution tells you how much solute is dissolved in the solvent.

Question 24

what is a saturated solution?

Answer 24

one in which no more solute will dissolve

Question 25

what is solubility?

Answer 25

solubility refers to the amount of solute that will saturate a particular solvent. solubility is specific for the type of solute and solvent.
solubility also varies with temperature.

Question 26

phase solubility rules (memorize)

Answer 26

the solubility of solids in liquids tends to increase with inc temp
the solubility of gases in liquids tends to decrease with increasing temp
the solubility of gas in liquids tends to increase with increasing pressure.
also keep in mind that the solubility of a gas in a liquid is also a function of the partial pressure of that gas above the liquid and the Henry’s law constant solubility =kP .
as partial pressure increases, the quantity of the dissolved gas increases as the equilibrium constant remains unchanged.

Question 27

solubility of salts in water (memorize)

Answer 27

all group 1’s and ammonium NH4+ salts are soluble.
all nitrate NO3- , perchlorate ClO4-, and acetate C2H3O2- salts are soluble.
all silver ag+, lead pb2+, pb 4+ and mercury Hg2+ salts are insoluble , except for their nitrates, perchlorate and acetates

Question 28

solubility product constant

Answer 28

the extent to which a salt will dissolve in water can be determined from its solubility product constant Ksp.
rem: at equilibrium, the solution is saturated. the rate at which ions go into solution is equal to the rate at which they precipitate out.

Question 29

what is the ion product?

Answer 29

ion product is the reaction quotient for a solubility reaction. Qsp!
Ksp = products of the concentrations of the ions in solution when the solution is saturated or at equilibrium.
Qsp: has exactly the same form as Ksp except the concentrations do not have to be at equilibrium

Question 30

what does the Qsp tell us?

Answer 30

Qsp more salt can be dissolved
Qsp=Ksp - solution is saturated
Qsp>Ksp -> excess salt will percipitate (reactants are favoured)

Question 31

Complex ions

Answer 31

complex ions consist of metallic ions surrounded by generally two, four, six ligands also known as lewis base (donated electrons)
these have different solubility properties as the addition of ligands can alter the solubility of simple metal salts.

Question 32

delta G= dela G under standard conditions +RTLnQ

Answer 32

REM: Q=K at equilibrium. and delta G= 0 at equilibrium
therefore the equation becomes:
0= delta G at standard conditions + RTLnKeq
delta G at standard conditions = -RTLnKeq

Question 33

what is the difference between delta G and delta G under standard conditions?

Answer 33

delta G is statement of spontaneity of a reaction in one direction or another.
Delta G under standard conditions is seen in its relation to Keq , a statement of the relative proportion of products and reactants at equilibrium.
- it describes the reaction at one specific temp, pressure, and set of concentration.
whereas delta G changes with changing reaction composition until it reaches zero.

Question 34

delta G standard <0, Keq>1 =

Answer 34

products are fav at equilibrium

Question 35

delta G standard =0, kEQ=1 =

Answer 35

Products and reactants are present in roughly equal amounts at equilibrium

Question 36

delta G standard >0, Keq<1 =

Answer 36

reactants are favoured.

Question 37

the difference between the heights of the reactants and products on any reaction coordinate diagram is ?

Answer 37

delta G standrad.