Equilibrium Flashcards
What is dynamic equilibrium?
Forward and backward rate of reaction are the same in a closed system. The concentration of product and reactant doesn’t change. This is because there is no matter transfer with the surroundings.
Give an example of a reversible reaction.
The Hrber process.
N2(g) + 3H2(g) <—-> 2NH3(g)
What is Le Chatelier’s principle?
If a change is made to a system in dynamic equilibrium, the position of the equilibrium moves to counteract this change.
How does change in temperature impact equilibrium?
Increase in temperature means the equilibrium moves in the endothermic direction to reverse the change.
Decrease in temperature means the equilibrium moves in the exothermic direction to reverse the change.
How does change in pressure impact equilibrium?
Increase in pressure means equilibrium shifts in direction that produces smaller number of gas moles to decrease the pressure.
Decrease in pressure means equilibrium shifts in direction that produces more moles of gas molecules to increase the pressure.
How does concentration impact equilibrium?
Increase in concentration means equilibrium shifts to right to reduce effect by increasing product concentration.
Decrease in concentration means equilibrium moves to left to reduce effect by increasing reactant concentration.
How does a catalyst impact equilibrium?
It has no effect on equilibrium position as it speeds up the rate of forward and backward reaction equally. This also means it has no effect on yield.
why are compromisees needed between yield and rate?
Changing temperature, concentration, pressure allows you to increase yield of desired products by changing equilibrium position. However, this can often take very long, or be expensive (pressure) so a compromise is made between temperature and yield as well as yield/speed and cost.
Consequently, a decent amount of product can be made quickly, allowing profit to be made.
Eg: Making Ethanol
C2H4(g) + H20 (g) <—-> C2H5OH(g)
∆H= -46KJmol-1
Decreasing temp moves equilibrium to the right, but this reaction is slow so a compromise temp of 300 degrees is chosen
High pressure shifts eq to right, increasing rate too. But thats expensive. compromise is 60 atm.
What does an equilibrium constant of more than 1 mean?
More products than reactants
What does it mean if equilibrium constant is less than one?
More reactants than products
What is equilibrium constant (Kc) worked out from?
The molar concentration in a reaction.
What is the kc expression?
[C]c [D]d
Kc= ————-
[A]a [B]b
Con of products to the power of their no. moles/ con reactants to the power of their no. moles
How do you find the units for Kc?
Write the top and bottom units of the molar concentrations and cancel them out. Invert the powers if the unit is under the line.
eg: 1/moldm-3 = mol-1dm3
