Chemical Equilibrium Flashcards
What is a reversible reaction
one in which the reactants react to form products that then react to give the reactants back
what is meant by chemical equilibrium?
the dynamic state where RATE OF the foward reaction is equil to the RATE OF the reverse reaction
Why is chemical equilibrium known as a dynamic state
the foward reaction and the reverse reaction continute to occour at the same time and do not stop
does a reaction at equilibrium cease? Explain
No - dymanic state, rate of foward reaction equals the rate of the reverse reaction
does the reaction being in equiibrium mean that the concentration of prodcuts and the reactant are the same?
No
if [products] greater than [reactants] - the equilibrium lies on the…..
right
if [reactants] greater than [ product]- equilibrium lies on the…
left
State Le chatelier’s principle
is a stress is applied to a system at equilibrium, the system shiftfs to oppose the applied stress
list three stresses that can be applied to a system at equilibrium
Temperture
Concentration
Pressure ( gasous reaction only)
Describe how concentartion alters a system at equilibrum
increasing a substances conc: Equilibrium will shift to decrease its concentration- in the dirction that uses it up
Decreasing a substance concentration Equilibrium will shift to increase conc - in the direction that produces more of it
so the reverse/foward reaction favoured to the left/right
Do Exothermic reactions produce heat or use up heat?
they produce heat - causing tempeture to rise
Do endothermic reactions produce heat or use up heat?
Endothermic reactions - use up heat - causing temperture drop
Describe how temperture alters a system at equilibrum
Increasing temperture :Equilibrium will shift to decrease temperture in the endothermic reaction
Decreasing temperture: **Equilibrium will shift to increase temperture in the exothermic direction to produce heat*
so the reverse/foward reaction favoured to the left/right
if the ΔH of a reversible reaction is negative…
THE FOWARD REACTION IS EXOTHERMIC
if the ΔH of a reaction is postive…
THE FOWARD REACTION IS ENDOTHERMIC
Under what conditions does pressure NOT have an effect of equilibrium
- If reaction is NOT a gaseous reaction
- If the molecules (molar ratio) are equal on each side of the equation
Describe the effects on equilibrium given that pressure affects the equilibrium
Increasing pressure: equilibrium will shift to decrease pressure in the direction that has less molecules
Decreasing pressure: Equilibrium will shift to increase presure in the direction that has more molecules
name a pratical way to decrease pressure
decrease container volume
What effect does a catalyst have on equilibrium? Explain
none, a catalyst brings a reaction to equilibrium more quickly but does not affect the sate of equilibrium. speeds up foward and reverse reqction equally
describe the procedure to investigate the effects of concentration
illustate Le Chatelier’s principle by demostrating the effects of both concentration changed and temperture changes on the reaction (Potassium thiocyanate) and iron III chloride
- use dropper to drop a drop of postassium Thioyanate to iron III chloride solution in a test tube
- red colour forms intially
- add dilute HCl
- Fe3+ decreases
- equilibrium shiftf to increase concentration of Fe3+ to produce more
- reverse reaction
- yellow colour forms due to formation of Fe3+
- add KCNS
- conc of CNS- increases
- equilibrium shiftf to use it up
- foward reaction favoured
- Red colour forms due to formation of Fe(CNS)+2
describe the procedure to investigate the effects of temperture
illustate Le Chatelier’s principle by demostrating the effects of both concentration changed and temperture changes on the reaction
- Using a dropper drop a drop of potassium thiocynate to iron (II) cloride
- Intially red colour forms due to formation of Fe(CNS)2+
- add sln to new test tube in beaker of hot water
- Temperture increases, equilibrium shiftf to decreasetemperture in endothermic direction to use up heay, reverse reaction favoured to the left
- **
- yellow colour forms due to formation of Fe3+
- add some new sln to a beaker of ie cold water
- temperture decreases.
- the equilibrium shidtd to increase temperture in the exothermic direction to produce heat
- red colour forms due to formation of Fe(CNS)+2
what is the sigificane of the intital red colour in this equilibrium mixture
illustate Le Chatelier’s principle by demostrating the effects of both concentration changed and temperture changes on the reaction
the equilibrium lies on the right.conc products>conc reactant
explain why changing the pressure has no effect on the equilibrium
illustate Le Chatelier’s principle by demostrating the effects of both concentration changed and temperture changes on the reaction
all the reactant and produts are in sln, presuress only affecrs equilibrium in gaseous equaltions
give two inductrial applications of Le chatelier’s principle
- manfacture of ammonia (Haber process)
2.manufacture of sulfuric acid (contact process)
According to Le Chatelier’s principle, what conditions should be used to maximise the yield of ammonia obtained?
High pressures and Low tempertures
why are the conditions according to Le Chatelier’s principle to maximise the yield of
ammonia obtained not used in practice
high pressures- costly (uneconimical), danger of gasleaks and explosions
low temperturs - rate of reaction is two slow
give three uses of ammonia
fertilizers, explosives, cleaning products
give three uses of sulfuric acid
car batteries
detergents
paints
What is meant by the equilibrium constant Kc?
the relationship between the concentration of the reactants and the products for a reaction at equilibrium
what is the formula for Kc?
Kc = [C][D] / [A][B] ( if the molar ration is not 1, put it as a power on the substance
What is the only stress that effects Kc
Temperature is the only factor that affects Kc Kc is always constant at constant temperature
Does concentration effect Kc?
No, Kc is always onstant at constant temperture
If Kc is greater than 1….
the concentration of products greater than the reactants- equilibrium lies on the right
If Kc is less than 1..
the concentration of reactants greater than products- equilibrium lies on the left
A increase in Kc means….
the foward reaction is being favoured (More products are being made)
a decrease in Kc means…
the reverse reaction is beging favoured(more reactants are being made)
What do the letters in and ICEE table stand for
Intial moles
(before reaction begins)
Change in moles
(use molar ratio)
Equilibrium moles
(then divide by volume (L) if given
Equilibrium molarilty
What is ment by a type one question
one in which you need to find the value of kc
What is meant by a type 2 question
one in whcih you know the value of kc and flind somthing else. You introduce kc
