6 Equilibria Flashcards
give two feauters of a reaction at equilibrium
the rate of the forward reaction is equal to the rate of the reverse reaction.This makes concentration of products and reactants appear constant
state Le chateliers principle
if a system at equilibrium is disturbed the equilibrium moves in the direction that tends to reduce the disturbance
give the meaning of the term dynamic equilibrium
the forward and backward recations proceed at equal rates.The concentration of reactants and products appear consatnt
state the effect of a catalyst on the time taken to reach equilibrium
increases the rate at reaching equilibrium
state the effect of a catalyst on the position of equilibrium
no affect
for what reaction is dynamic equilibrium achieved
for a reversible reaction in a closed system so no reactants/products are able to escape
state and explain what happens to the yield of methanol when the total pressure is increased
CO2(g) + 3H2(g) ⇌ CH3OH(g) + H20(g)
if you increase the pressure equilibrium will try and decrease the pressure so it moves to the side with fewer moles of gas which in this case is to the right and so increases the yield of methanol
state and explain what happens to the yield of methanol when the total pressure is increased
CO2(g) + 3H2(g) ⇌ CH3OH(g) + H20(g)
if you increase the pressure equilibrium will try and decrease the pressure so it moves to the side with fewer molecules of gas which in this case is to the right and so increases the yield of methanol
use le chateliers principle to explain why the mixture of gases becomes darker in colour when the mixture is heated at constant pressrue
N204(g) ⇌ 2NO2(g) ΔH=+58 kJ/mol
if temoerature increases equilibrium will try and decrease it so it shifts to the endothermic direction to absorb the heat which in this case is to the right and so the mixture of gases becomes darker
use Le chateliers principle to explain why the amount of NO2 decreases when the pressure is increased at constant temperautre
N204(g) ⇌ 2NO2(g) ΔH=+58 kJ/mol
if you increase the pressure equilibrioum will try and decrease it and so it shifts to the side with fewer gas molecules which is to the left and so the yield of N2O4 increases and the yield of NO2 decreases
use le chateliers principle to explain the effect of an increase in pressure at constant temperature on the yield of ammonia
N2(g) + 3H2(g) ⇌ 2NH3(g)
when you increase the pressure equilibrium will try and decrease it so it shifts to the side with fewer gas molecules which in this case is to the right and so increases the yield of ammonia
use le chateliers principle to explain the effect of an increase in temperature at constant pressure on the yield of ammonia.(forward recation is exothermic)
N2(g) + 3H2(g) ⇌ 2NH3(g)
when you increase the temperautre equilibrium will try and decrease it so it moves to the endothermic dircetion to try and abosrb the heat which in this case is the left side and so decreases the yield of ammonia
what happens when you increase the concentration of a reactant on the yield of products
when you increase the concenctration of the reactants equilibrium will try and make more product so the equilibrium shifts the right and so increases the yield of products
what happens when you decrease the concentration of a reactant on the yield of products
when you decrease the concenctration of the reactant equilibrium will try and increase the concentration of the reactnat so the equilibrium shifts the left and so decreases the yield of products
what happens to the position of equilibrium when you increase the pressure
equilibrium will try and dcerease the pressure and so shifts to the side fewer gas molecules
what happens to the position of equilibrium when decrease the pressure
equilibrium will try and increase the pressure and so shifts to the side with more gas molecules
what happens to the position of equilibrium when you increase the temperature
equilbriums will try and decrease the temperatutre and so shifts in the endothermic directions(positive ΔH) direction to abosrb the heat
what happens to the position of equilibrium when you decrease the temperature
equilibrium will try and increase the temperature and so shifts in the exothermic (negative ΔH) direction to produce more heat
what is the Kc value
Kc is a calculated value that tells us whether a reaction lies more towards the products side or the reactants side.If Kc is greater than zero equilibrium lies more on the products side.If Kc is less than zero equilibrium lies more towards the reactants side
In industry, a fermentation reaction is carried out at 35 °C rather than 25 °C.
Suggest one advantage and one disadvantage for industry of carrying out the
fermentation at this higher temperature.
advantage: ethanol is produced at a faster rate
disadvantage: more eneergy is required in the reaction
explain why, for a reversible reaction used in an industrial process, a compromise temperature 300*C may be used.
C2H4 + H20 ⇌ C2H5OH ΔH = -46 kj/mol
300C is a compromise because this is an exothermic reaction lower temperatures favour the forward reaction so you get a better yield of ethanol but lower temperatures means a slower rate of reaction so a 300C is a compromise between a reasonable yield and a faster reaction
explain why, for a reversible reaction used in an industrial process, a compromise pressure of 60-70 atmopsheres may be used.
C2H4(g)+ H20(g) ⇌ C2H5OH(g) ΔH = -46 kj/mol
high pressure shifts the equilibrium to the side with fewer gas moles which is to the right increasing the yield of ethanol also a high pressure increases the rate of reaction however a very high pressure is really expensive to produce as you need strong equipment to withstand high pressures.So a 60-70 atmospheres is a compromise it gives a reasonable yield for the lowest possible price.
how do you set up your workings for a question based on calculating Kc
elements ⇌ elements ratio: initial no.moles: change: final/equilibrium no. moles:
the change will vary on the sign(+ or -) and the ratio of moles whatever the change is on the right hand side is opposite sign to the change on the left hand side
what is the Kc expression for this reaction 2HI ⇌ H2 + I2
Kc =[H2][I2] / [HI]^2
what is the Kc units for this reaction 2HI ⇌ H2 + I2
make moldm^-3 x
(x)(x)/(x)2
= x^2/ x^2
=1 therfore no units
what is the Kc expression for this reaction
2CHCLF2 ⇌ C2F4 + 2HCL
Kc=[C2F4][HCL]^2 / [CHCLF2]^2
what is the Kc units for this reaction
2CHCLF2 ⇌ C2F4 + 2HCL
make moldm^-3 x (x)(x)^2 /(x)^2 =x^3/x^2 =x moldm^-3
state and explain the effect,if any, of adding a catalyst to the value of Kc
no affect because a catalyst increases the rate of the forward reaction and the reverse recation equally
state t and explain the effect,if any, of changing the concentration to the value of Kc
no affect because concentraion appears constant
state and explain the effect,if any, of increasing the temperature to the value of Kc for an exothermic reaction
decreases the value of Kc
state and explain the effect,if any, of increasing the temperature to the value of Kc for an endothermic reaction
increases the value of Kc
for decreasing the temperature for an endothermic reaction state: the temperature change effect on Kc effect on products effect on reactants direction of change of equilbrium
tempertaure change:decrease effect on Kc:decrease effect on products:decrease effect on reactants:increase direction of change of equilibrium:moves left
for increasing the temperature for an endothermic reaction state: the temperature change effect on Kc effect on products effect on reactants direction of change of equilbrium
tempertaure change:increase effect on Kc:increase effect on products:increase effect on reactants:decrease direction of change of equilibrium:moves right
for increasing the temperature for an exothermic reaction state: the temperature change effect on Kc effect on products effect on reactants direction of change of equilbrium
temperature change:increase effect on Kc:decrease effect on products:decrease effect on reactants :increase direction of change of equilbrium:moves left
for decreasing the temperature for an exothermic reaction state: the temperature change effect on Kc effect on products effect on reactants direction of change of equilbrium
temperature change:decrease effect on Kc:increase effect on products:increase effect on reactants :decrease direction of change of equilbrium:moves right
state the general equation for Kc
[products] / [reactants]
