Equilibrium Flashcards
What is Kc
equilibrium constant, has a fixed value at a specific temperature
What is the equilibrium constant expression?
write it down on paper
high value of Kc
equilibrium lies to right, favors production of products, reaction almost completed
low value of Kc
equilibrium lies to left, favors reactants, reaction barely started
What is the purpose of the constant Kc?
to inform us of the nature of equilibrium (where it lies). But, it doesn’t tell us how quickly the equilibrium state is reached
If Q=Kc, Q>Kc, Q
- Q=Kc: equilibrium is reached
- Q>Kc: proceed to favor reactants, shift to left
- Q
What is the value of Kc in an inverse reaction?
Kc’, 1/Kc, Kc-1
What is the value of Kc in a multiple of a reaction?
Kc^x
What is the value of Kc when the reaction coefficients are halved?
square root Kc
What is the value of Kc when two reactions are added together?
Kc^i x Kc^ii
What do industries use equilibrium for?
to determine conditions that will maximize the yield of a product
evaporation
liquid to vapour state
condensation
vapour to liquid
dynamic equilibrium
forward and backward reactions are still occurring even though it doesn’t look like it
Forward reaction
left to right, reactants to products
Backward reaction
right to left, products to reactants
Specific characteristics of equilibrium (5)
- dynamic
- achieved in closed system so no exchange of matter with surroundings
- concentrations of reactants and products remain constant because they’re being produced and destroyed at an equal rate
- no change in macroscopic properties because concentration is constant (color or density)
- can be reached from either direction
Le Chatelier’s principle
system at equilibrium when subjected to a change will respond in such a way to minimize the effect of the change
What happens when the concentration of a reactant increases?
- forward reaction increases, rate of reactions no longer equal
- at equilibrium, equilibrium favors production of products, shifts to right
What happens when a product is removed or it decreases in concentration?
- backward reaction decreases, rate of reactions no longer equal
- equilibrium favors production of product, shift to right
What happens when pressure is increased?
equilibrium shifted to side with smaller number of particles
What happens when pressure is decreased?
equilibrium shifted to side with greater number of particles
Exothermic reactions
- temperature always decreases
- enthalpy negative
- favors production of products, equilibrium shifts to right
- product particles don’t have enough energy to form bonds
- takes less energy to form bonds with products
- increased value of Kc
Endothermic reactions
- temperature always increases
- enthalpy positive
- favors production of reactants
- equilibrium shifted to left
- decreased value of Kc
- takes less energy to break bonds than it does to make them
Where does equilibrium shift for exothermic reactions?
to the right, higher yield of products at a lower temperature
Where does equilibrium shift for endothermic reactions?
to the left
Effect of concentration, pressure, temperature, catalyst on Kc
nothing changes the value except temperature
What is one dilemma we come across with exothermic reactions?
at a lower temperature, there is a lower rate of reaction, and it takes longer to produce a high yield of products
What does a catalyst do? How do they affect the equilibrium state?
- speeds of rate of reaction by providing alternate reaction pathway with a lower activation energy
- not chemically changed after reaction
- speed up attainment of equilibrium state by making products form faster
Draw and label an energy diagram
Label:
- Ea of forward and backward reaction
- reactants and products
At high temperatures, the _______ reaction is favored. At low temperatures, the ______ reaction is favored.
- high temp= endothermic
- low temp= exothermic
At high temperatures, the _______ reaction is favored. At low temperatures, the ______ reaction is favored.
- high temp= endothermic
- low temp= exothermic
What is the goal for industrial companies in their processes?
- high rate of reaction
- equilibrium lies to the right to produce high yield of products
Draw the reaction the haber process is based upon.
N2+ 3H2 +_ 2NH3
Is the forward reaction of the haber process exothermic or endothermic?
exothermic
Three key things to know for the Haber process:
- reactants and products are gases
- change in number of gas molecules as reaction proceeds
- forward reaction is exothermic, backwards is endothermic
How is concentration used to benefit industries? Haber process.
- nitrogen and hydrogen have 1:3 ratio
- ammonia is removed once it forms, causing equilibrium to shift to right to favor products
How is pressure used to benefit industries? Haber process.
- because there are less molecules on the right than the left( 2 on right, 4 on left), favored by high pressure
- more ammonia made
- optimum pressure: 2 x 10^7
Optimum pressure for haber process
2 x 10^7
How is temperature used to benefit industries? Haber process.
- forward reaction exothermic, so favored by lower temperature
- moderate temperature of 450 degrees
Temperature of Haber process
450 degrees
Catalyst of Haber process
iron with small amounts of aluminum and magnesium oxides
Catalyst of Haber process
iron with small amounts of aluminum and magnesium oxides
Write out the three steps of the Contact Process with equations.
- Combustion of sulfur to form sulfur dioxide
- Sulfur dioxide oxidizes to form sulfur trioxide.
- Sulfur trioxide reacts with water to form sulfuric acid.
Is the forward process of the Contact Process exothermic or exothermic?
exothermic
Describe pressure of Contact Process to create sulfuric acid.
- 3 molecules on right and 2 on left, reaction favored by high pressure
- equilibrium shifts to right
- produces more sulfur trioxide
- 2 x 10^5 Pa
Describe temperature of Contact Process to create sulfuric acid.
- forward reaction exothermic
- moderate temperature of 450 degrees celsius
Describe catalyst of Contact Process to create sulfuric acid.
Vanadium (V) Oxide
Too low a temperature for processes does what?
increase the yield, but decrease the rate at which it produces yield
What is the pressure of the Contact process?
2 x 10^5
Pressure of methanol production
- 5-10 x 10^6 Pa
- 3 to 1 molecules means high pressure will favor product
- equilibrium shifts to right
Temperature of methanol production
- forward reaction is exothermic
- 250 degrees celsius
Catalyst of methanol production
- Cu - Zno - Al2O3
