Equilibrium Flashcards
Open System
Matter can also be exchanged with the surroundings
Closed system
No matter (only energy) is exchanged with the surroundings
Examples of reversible processes (3)
Evaporation and condensation of water in a sealed bottle
Dissolving and crystallisation taking place in a saturated solution
Reaction between ethanoic acid and water in a sealed bottle of vinegar
When does a closed chemical system reach a state of chemical equilibrium?
When the rate of the forward reaction is equal to the rate of the opposite reaction.
What occurs in a system at chemical equilibrium? (2)
The amounts of the reactant and product species remain constant and so its observable properties (temperature, pressure, colour etc) of the system are also constant.
Reaction continues but there is no net reaction since the rate of the forward reaction is equal to the rate of the reverse reaction
What occurs in a system at chemical equilibrium? (Observable properties)
The amounts of the reactant and product species remain constant and so its observable properties (temperature, pressure, colour etc) of the system are also constant.
What occurs in a system at chemical equilibrium? (net reaction)
Reaction continues but there is no net reaction since the rate of the forward reaction is equal to the rate of the reverse reaction
Do open systems reach a state of equilibrium
No
Equilibrium constant (Kc)
The relationship between the equilibrium concentrations of the reactant s and products at a particular temperature has a constant value
What is the general reaction for the equilibrium constant? aA + bB ⇄cC + dD
Kc = [C]ⁿ [D]ⁿ / [A]ⁿ [B]ⁿ
State the Le Chatelier’s Principle
If a system at equilibrium is subjected to a change in conditions, the system will adjust to re-establish equilibrium in such a way as to partially counteract the imposed change.
What are the 4 additions that can change a system that is already at equilibrium?
Change in concentration
Change in Temperature
Change in Volume/Pressure of a Gaseous system
Addition of a Catalyst
What occurs to a system at equilibrium when concentration of reactants is increased?
The forward reaction will speed up to use up some of the extra reactants. The reverse reaction rate then also increases and eventually catches up until both rates are equal again.
Therefore, some of the extra reactants will have been used up, and the concentration of products will be more than before.
What occurs to a system at equilibrium when the concentration of the products is increased?
The reverse reaction will speed up to use up some of the extra products will have been used up, and the concentration of reactants will be more than before
What occurs to a system at equilibrium when temperature changes? (increased)
If the temperature is increased, net reaction will proceed in the direction that absorbs heat (endothermic direction).
What occurs to a system at equilibrium when temperature changes? (decreased)
If temperature is decreased, net reaction occurs in the direction that releases heat (exothermic)
What occurs to a system at equilibrium when volume/pressure of a gaseous system changes?
The volume of a gas is indirectly proportional to the pressure it exerts.
What occurs to a system at equilibrium when volume/pressure of a gaseous system changes? (volume increases)
Increasing the volume of a gaseous system at equilibrium, results in a decrease in pressure, net reaction proceeds in the direction that produces the greatest number of particles.
What occurs to a system at equilibrium when volume/pressure of a gaseous system changes? (pressure)
If pressure is increased, volume decreases, net reaction occurs in the direction that produces the least number of particles.
What occurs to a system at equilibrium when a catalyst is added? (already at equilibrium)
Adding a catalyst to a system that is already at chemical equilibrium will have no effect on the system.
What occurs to a system at equilibrium when a catalyst is added? (not at equilibrium)
A catalyst added to a system NOT at equilibrium will speed up the rate at which equilibrium is established
Position of equilibrium
The relative amounts of reactants and products at equilibrium
What are the 3 conditions that the position of equilibrium may be changed by, for any equilibrium system?
Adding or removing a reactant or product
Changing the pressure by changing the volume (for equilibria involving gases)
Diluting (for equilibria in solution)
Changing the temperature
Total Pressure =
Total Pressure=Sum of the partial pressures of all gases in the mixture
4 macroscopic (observable and measurable) properties that remain constant
Concentrations of reactants and products
Temperature
Pressure
Colour
How does agitation increase the reaction rate. Explain using collision theory. (NaCl and H2O)
agitation assists in the collisions breaking the bonds between NaCl through dissociation. Creating ion-dipole forces between H2O and Na+ and Cl-.
Extent of reaction
Describes how much product is formed when the system reaches equilibrium
Rate of reaction
measure of the change in concentration of the reactants and products with time and is not directly related to the extent of reaction
What is the general reaction for the Reaction quotient?
Q = [C]ⁿ [D]ⁿ / [A]ⁿ [B]ⁿ
At equilibrium what value to the reaction quotient and equilibrium constant have in common
Their values are equal
In general, for chemical reactions at equilibrium: (3)
Different chemical reactions have different values of Kc
The size of Kc indicates the proportions (relative amounts) of reactants and products in the equilibrium mixture
For a reaction, Kc is constant for all equilibrium mixtures at a fixed temperature.
In general, for chemical reactions at equilibrium: (different)
different chemical reactions have different values of Kc
In general, for chemical reactions at equilibrium: (size of Kc)
the size of Kc indicates the proportions (relative amounts) of reactants and products in the equilibrium mixture
In general, for chemical reactions at equilibrium: (Temperature)
for a reaction, Kc is constant for all equilibrium mixtures at a fixed temperature.
Homogeneous reactions
All products and reactants are in the same state or phase
Heterogenous reactions
Products and reactants are in different states of phases
If Kc<1 then….
There are more reactants than products
If Kc>1 then…
There are less reactants than products
One difference between Kc (Equilibrium constant) and Q (reaction quotient)
Q (reaction quotient) can be measured anytime during the reaction. Kc cannot as you are only measuring the Equilibrium.
What is the only thing that can change the value of the Kc
TEMPERATURE
What happens when temperature is increased for an exothermic reaction?
the value for Kc decreases and so the amount of products present at equilibrium decreases
What happens when temperature is increased for an endothermic reaction?
the value of Kc increases and so the amount of products present at equilibrium increases
What occurs to vapour pressure when the rate of evaporation is equal to the rate of condensation?
it will remain constant (molecules leaving is equal to molecules re-entering; so molecules in space above liquid remains constant)
What are 2 things that an equilibrium system be upset by?
changing the concentration of any of the reactants or products (gases or solutes, but not solids liquids)
changing the temperature
Increase the concentration of reactants (Le Chatelier)
If more reactants is added to an equilibrium system, the system will adjust to decrease the concentration (and partial pressure)
Decrease the concentration of one of the substances
It’ll be favoured to increase the concentration of that substance
For reactions involving gases. Increase the system volume, decrease in pressure
Increases the number of gas molecules, by favouring the side that has more molecules. The extra molecules produced increase the pressure again
For reactions involving gases. Decrease the system volume, increase in pressure (Le Chatelier)
As there is an increase in pressure, the partial pressures of all gases increase simultaneously, as do with concentrations. Therefore, the position of equilibrium will move in the direction of the fewest gas particles
Increase the temperature (adding heat)
Direction that uses up heat (endothermic) is favoured
Decrease the temperature (remove heat)
Direction that produces heat (exothermic) is favoured
Increase the concentration of reactants (Collision theory)
Increased reactants, the forward reaction initially becomes greater than the rate of the reverse reaction as more frequent collision are occurring.
What happens overall to the equilibrium when an increase in concentration of reactants occur?
Overall, a net forward reaction has occurred with an increase in the concentration and partial pressure of the product at equilibrium.
The equilibrium has shifted to the right.
Increasing the concentration of products
Increases the formation of reactants, increasing the rate of the reverse reaction, due to more frequent collisions occurring between products. Equilibrium shifts left
Decreasing the concentration of products
Increases the formation of products (net forward reaction). Equilibrium shifts right
For reactions involving gases. Decrease the system volume, increase in pressure (collision theory)
As the volume decreases, at first since the gases are all closer together more collisions between gas molecules. This is then counteracted by the side that has the least amount of molecules produced. As the amount of molecules decreases, the pressure decreases, a new equilibrium is established
Adding an inert gas (Le chatelier)
presence of additional gas does not change any of the concentrations of reactants and products, there is no effect on the position of the equilibrium or Kc
Adding an inert gas (collision theory)
collisions with inert gas molecules will not produce a reaction so no net reaction occurs but increases the pressure as there have been more molecules added to the mixture
Diluting a mixture
adding water reduces the number of particles per volume. It results in a shift in the position of equilibrium towards the side that produces the greater number of dissolved particles. momentarily lowering the concentration of each species
Increasing the temperature (exothermic) (collision theory)
Molecules move faster and more frequent and energetic collisions. more molecules now have the necessary activation energy to undergo successful collisions
At higher temps, the rates of both the forward and reverse reactions increases.
As the endothermic reaction has a greater activation energy than the exothermic reaction. The rate of this reaction will increase more than the rate of the exothermic reaction.
When the system re- establishes equilibrium at a higher temperature, the new equilibrium has a higher concentration of reactants and a lower concentration of products.
Increasing the temperature (endothermic)
All reactants and product molecules have more energy and move faster. Increased temperature favours the endothermic reaction and the net reaction goes in the direction of the endothermic reaction
Haber Process
3H2 (g) +N2(g) ⇄ 2NH3(g) ∆H=-92kJmol-1
What are the 3 main stages of the Haber process?
N2 and H2 are compressed to between 10 and 25MPa of pressure in a compressor.
Compressed gases are pumped into the converter where reaction takes place (equilibrium is established) at temp of 350º and 550ºC.
Equilibrium mixture is then pumped into a condenser where only the ammonia liquifies and is removed. Unreacted Hydrogen and Nitrogen are recycled back into the converter
4 Compromises made when making ammonia in commercial quantities using the Haber process
The reactants are introduced into the converter in stoichiometric ratio
Pressures of 100 - 250 atmospheres (10-25 MPa) are used to maximise ammonia production while keeping operating costs as low as possible and maximising safety.
Temperatures between 350oC and 550oC are used to maximise reaction rate without lowering the yield too much
The catalyst used is a porous iron oxide that maximises contact with the reactants.
What are the optimum conditions for CH4(g) +H2O(g) ⇄ CO(g) + 3H2(g) ∆H=+206kJmol-1 to get the highest amounts of H2 gas? (pressure)
Low pressure favours the formation of H2 (forward reaction and desired product) but slows down the reaction rate (less effective collisions at lower pressure)
Pressure = 1-2 MPa
What are the optimum conditions for CH4(g) +H2O(g) ⇄ CO(g) + 3H2(g) ∆H=+206kJmol-1 to get the highest amounts of H2 gas? (temperature)
High temperature favours the forward (endothermic) reaction resulting formation of hydrogen AND faster reaction rate
What are the optimum conditions for CH4(g) +H2O(g) ⇄ CO(g) + 3H2(g) ∆H=+206kJmol-1 to get the highest amounts of H2 gas? (catalyst)
Using a Nickle catalyst will increase reaction rate (but not affect yield of hydrogen).
What are the optimum conditions for CO(g) +H2O(g) ⇄ CO2 (g) + H2(g) ∆H=-41kJmol-1 to get the highest amounts of H2 gas? (pressure)
High pressure has no effect on how much hydrogen (desired product) is formed, however high pressure increases the rate of collisions and hence the rate of reaction.
Pressure = 1-2 MPa
What are the optimum conditions for CO(g) +H2O(g) ⇄ CO2 (g) + H2(g) ∆H=-41kJmol-1 to get the highest amounts of H2 gas? (temperature)
Low temperatures favour the forward reaction (exothermic process) but also decreases the rate of reaction.
Temperature = 200C-500C
What are the optimum conditions for CO(g) +H2O(g) ⇄ CO2 (g) + H2(g) ∆H=-41kJmol-1 to get the highest amounts of H2 gas? (catalyst)
Using a Nickel catalyst will increase reaction rate (but not affect yield of hydrogen).
What are the two processes used to create H2 gas?
steam reforming
CH4(g) +H2O(g) ⇄ CO(g) + 3H2(g) ∆H=+206kJ mol
‘shift’ reaction.
CO(g) +H2O(g) CO2 (g) + H2(g) ∆H=-41kJmol
What are the optimum conditions for 3H2 (g) +N2(g) ⇄ 2NH3(g) ∆H=-92kJmol-1 to get the highest amounts of NH3 gas? (temperature)
Low temperatures favour the forward reaction (exothermic process) but also decrease the rate of reaction.
Temperature = 350C-550C
What are the optimum conditions for 3H2 (g) +N2(g) ⇄ 2NH3(g) ∆H=-92kJmol-1 to get the highest amounts of NH3 gas? (pressure)
High pressure favours the formation of ammonia AND increases the rate of reaction (high pressure increases the rate of collisions).
Pressure = 10-25 MPa
What are the optimum conditions for 3H2 (g) +N2(g) ⇄ 2NH3(g) ∆H=-92kJmol-1 to get the highest amounts of NH3 gas? (catalyst)
Using a catalyst will increase reaction rate (but not affect yield of ammonia).
What is the equation for steam reforming?
CH4(g) +H2O(g) ⇄ CO(g) + 3H2(g) ∆H=+206kJ mol
What is the equation for the ‘shift’ reaction?
CO(g) +H2O(g) CO2 (g) + H2(g) ∆H=-41kJmol
Why does the nickel catalyst need to be replaced regularly?
Carbon monoxide and carbon dioxide are poisons for the nickel catalyst and so nickel needs to be replaced regularly for optimum results
What is an alternate way of reusing the CO2 created?
The carbon dioxide can be used up instead for refining of bauxite to alumina
Why are pressures kept low?
if the pressure is too high cost-effectiveness and safety are compromised, as high pressures may cause explosions due to there being an increase in collisions with the walls of the container
Why is the same amount of pressure used for steam reformation and the ‘shift’ reaction?
the same pressure as for the previous reaction is used as it is cost-effective to maintain the same pressure
Why is the unreacted gases recycled and ammonia removed?
By removing ammonia and recycling the unreacted gases, ammonia product can occur at a relatively constant rate provided nitrogen and hydrogen are compressed and pumped into converter at a constant rate
What are the three main stages of the contact process?
- The conversion of sulfur to sulfur dioxide by burning elemental sulfur in air at around 1000C
- The conversion of sulfur dioxide to sulfur trioxide in a catalytic converter tower.
- The conversion of sulfur trioxide and water to sulfuric acid which is achieved indirectly by initially absorbing gaseous SO3 into 98% pure liquid H2SO4.
What is the first stage of the contact process?
The conversion of sulfur to sulfur dioxide by burning elemental sulfur in air at around 1000 oC.
S(l) +O2(g) ⇄ SO2(g) ∆H=-297kJmol-1
What is the second stage of the contact process?
The conversion of sulfur dioxide to sulfur trioxide in a catalytic converter tower. 2SO2(g) +O2(g)⇄ 2SO3(g) ∆H=-196kJ mol-1
What is the third stage of the contact process ?
conversion of sulfur trioxide and water to sulfuric acid which is achieved indirectly by initially absorbing gaseous SO3 into 98% pure liquid H2SO4.
H2SO4 (l) + SO3 (g)⇄ H2S2O7 (l) + H2O (l)
H2S2O7 (l)⇄ 2 H2SO4 (l)
overall SO3 (g) + H2O(l) mol-1 ⇄ H2SO4 (l) ∆ H = - 88 kJ
What are the three reactions that occur in the third stage of the contact process?
H2SO4 (l) + SO3 (g)⇄ H2S2O7 (l) + H2O (l)
H2S2O7 (l)⇄ 2 H2SO4 (l)
overall SO3 (g) + H2O(l) mol-1 ⇄ H2SO4 (l) ∆ H = - 88 kJ
What are the optimum conditions for 2SO2 (g) + O2 (g) ⇄ 2SO3 (g) ∆ H = - 196 kJ mol-1 to get the highest amounts of SO3 gas? (temperature)
Low temperatures favour the forward reaction (exothermic process) but also decreases the rate of reaction.
Temperature = 400C-500C
What are the optimum conditions for 2SO2 (g) + O2 (g) ⇄ 2SO3 (g) ∆ H = - 196 kJ mol-1 to get the highest amounts of SO3 gas? (pressure)
High pressure favours the formation of sulfur trioxide AND increases the rate of reaction (high pressure increases the rate of collisions).
Pressure = just above atmospheric pressure (101.3 kPa)
What are the optimum conditions for 2SO2 (g) + O2 (g) ⇄ 2SO3 (g) ∆ H = - 196 kJ mol-1 to get the highest amounts of SO3 gas? (catalyst)
Using a catalyst will increase reaction rate
For the reaction SO3 (g) + H2O(l) mol-1 ⇄ H2SO4 (l) ∆H= -88 kJ why must the temperature be not too high?
As since the reaction is a highly exothermic reaction it can get too dangerous if H2SO4 begins boiling and turning into gas, making it toxic
Where does the SO2 they use for the reaction come from?
Either SO2 as a waste product of the nickel refining process or SO2 produced by the burning of sulfur in air and excess heated air in a converter
What are the 5 steps for the creation of H2SO4?
- Mixture of the two SO2 gases are passed over a porous bed of vanadium pentoxide catalyst and some of the SO2 converts to SO3 and the temperature rises to over 600C.
- Gas mixture is then cooled by pumping it back out of the converter and using the excess heat to heat the incoming air. The cooled mixture is then pimped back into the converter and passed over a second catalyst bed.
- Gases are removed again and cooled before returning to the converter and is passed over a third catalyst bed. The mixture would now contain a high percentage of SO3
- The gas mixture is then pumped into the base of an absorption tower where 98% pure sulfuric acid is sprayed in from the top. The rising gas mixture meets the concentrated acid, resulting in only the sulfur trioxide dissolving in the 2% of water present
The resulting liquid is effectively 100% pure sulfuric acid. - Any SO2 and air that is present rises to the top and is recycled back to the converter.
What is the first process that occurs in the creation of H2SO4?
- Mixture of the two SO2 gases are passed over a porous bed of vanadium pentoxide catalyst and some of the SO2 converts to SO3 and the temperature rises to over 600C.
What is the second process that occurs in the creation of H2SO4?
- Gas mixture is then cooled by pumping it back out of the converter and using the excess heat to heat the incoming air. The cooled mixture is then pimped back into the converter and passed over a second catalyst bed.
What is the third process that occurs in the creation of H2SO4?
- Gases are removed again and cooled before returning to the converter and is passed over a third catalyst bed. The mixture would now contain a high percentage of SO3
What is the fourth process that occurs in the creation of H2SO4?
- The gas mixture is then pumped into the base of an absorption tower where 98% pure sulfuric acid is sprayed in from the top. The rising gas mixture meets the concentrated acid, resulting in only the sulfur trioxide dissolving in the 2% of water present
The resulting liquid is effectively 100% pure sulfuric acid.
What is the fifth process that occurs in the creation of H2SO4?
- Any SO2 and air that is present rises to the top and is recycled back to the converter.
What occurs to the pure sulfuric acid after all 5 steps?
The pure sulfuric acid is carefully diluted back to 98% for storage, transport and use. Some of the 98% sulfuric acid is sent back to the absorption tower
When does equilibrium occur in the carbon cycle?
An equilibrium exists when the rates at which the amounts of carbon enters and leaves a stages in the carbon cycle are equal
How does Global warming affect equilibrium levels in the carbon cycle?
Global warming causes an increase in the levels of atmospheric greenhouse gases, due to the use of fossil fuels and because of this the equilibrium is disrupted due to there being an increase in carbon, resulting in an increased proportion of greenhouse gases an increase in the average temperature occurs due to increased infrared radiation absorbed and re-radiated back towards the earth
Why is salt water slightly basic?
due to the presence of dissolved carbonate ions in the water, as dissolved carbonate ions can react with the water to form hydrogencarbonate and hydroxide ions.
What is Calcification?
precipitation of dissolved calcium and carbonate ions as calcium carbonate in the form of shells and corals.
What is the difference between a chemical equilibrium and a physical equilibrium?
In chemical equilibrium bonds are constantly breaking and forming while at a physical equilibrium substances are changing states constantly.
What are 3 constant macroscopic properties of a system once equilibrium is attained? (4)
The amounts of the reactants
The amounts of the products
Temperature
Pressure
Why is sulfur trioxide dissolved in concentrated sulfuric acid rather than just being mixed with water?
as it the reaction between eater and sulfur trioxide is very exothermic, that if the H2SO4 boils turning into gas it can become very dangerous
One way the heat produced in the contact process can be used to become more economical.
The heat energy released can be used to increase the rate of the next step of the process, particularly the heat evolved from the production of SO2.
Why do both reactions speed up at first when the volume is reduced?
As both rates increase due to increased partial pressures and concentrations
Why do both reactions slow down at first when the temperature is decreased?
Both reaction rates slow down due to less K.E of particles at lower temp and therefore fewer particles with energy less than activation energy
What are the four reactions that occur in calcification?
CO₂(g) ⇌ CO₂(aq)
CO₂(aq) + H₂O ⇌ HCO₃⁻(aq) + H⁺(aq)
HCO₃⁻(aq) ⇌ CO₃⁻²(aq) + H⁺(aq)
Ca²⁺(aq) + 2HCO₃²⁻(aq) ⇌ CaCO₃(s) + CO₂(aq) + H₂O(l)
What would the effect on the equilibrium if a solid is added?
No effect as solids do not effect the equilibrium concentration of reactants
Carbon disulfide is removed from the reaction vessel on a regular basis. Using collision theory, explain how this technique will increase the yield of the reaction.
2SO₃ + CO₂ ⇄ CS₂ +4O₂
The concentration of the carbon disulfide is continually reduced which reduces the rate of the reserve reaction due to less collisions between the CS₂ and O₂. The rate of the forward reaction is not affected. There is a net forward reaction favoured increasing the products (+yield) and equilibrium shifts to the right
Second step of calcification CO₂(aq) + H₂O
CO₂(aq) + H₂O ⇌ HCO₃⁻(aq) + H⁺(aq)
First step of calcification CO₂(g)
CO₂(g) ⇌ CO₂(aq)
Third step of calcification HCO₃⁻(aq)
HCO₃⁻(aq) ⇌ CO₃⁻²(aq) + H⁺(aq)
Fourth step of calcification Ca²⁺(aq) + 2HCO₃²⁻(aq)
Ca²⁺(aq) + 2HCO₃²⁻(aq) ⇌ CaCO₃(s) + CO₂(aq) + H₂O(l)
