Kinetics Flashcards
When does dynamic equilibrium occur?
When you have a reversible reaction in a close system (nothing can be added to the system or taken away from it, apart from energy )
Features of dynamic equilibrium:
- a reversible, chemical reaction is a dynamic process
- Position of equilibrium can be varied by changing certain conditions
- Everything may appear stationary, but if reactions are moving both ways
What happens to the quantity at equilibrium?
At Equilibrium the quantities in the mixture stays constant, though the reactions are still continuing. Rates of forward and back reactions are equal.
What is homogeneous equilibrium?
When Products and reactants are in the same phase
What is heterogeneous equilibrium?
When products and reactants are in more than one phase/different phase
What is le Chateliers principal?
When a change is applied to a system in dynamic equilibrium, the system reacts in such a way as to oppose the effect of the change
What factors affect the position of equilibrium?
- Concentration
- Pressure
- Temperature
How does concentration affect the position of equilibrium?
- A change in the concentration of reactants will also the rate of a forward reaction
- A change in concentration of products will alter the rate of a reverse reaction
How can you shift the equilibrium to the right with concentration?
- Increase the concentration of reactants
- Reduce the concentration of product
How can you shift the equilibrium to the left with concentration?
- Decrease the concentration of reactants
- Increase the concentration of products
What effect does pressure have when moles of gas are equal on both sides?
No change
What happens to equilibrium when you increase pressure?
Move to the side with fewer gaseous molecules
What happens to equilibrium when you decrease pressure?
Move to the side with more gaseous molecules
definition of dynamic equilibrium
a steady state, where the rates of the forward and reverse reaction are the same
definition of a steady state
when the conc of the reactants and products remain constant
what happens when you increase temp in an exothermic reaction
equilibrium moves to the left
what happens when you decrease temp in an exothermic reaction
equilibrium moves to the right
what happens when you increase temp in an endothermic reaction
equilibrium moves to the right
what happens when you decrease temp in an endothermic reaction
equilibrium moves to the left
what effect does catalysts have on equilibrium?
- increases rate of attainment of equilibrium
- does not affect the position of equilibrium
- speed up industrial equilibrium reactions
what is the equation for the haber process
N2(g) + 3H2(g) <=> 2NH3(g)
= -92kj/mol
what are the conditions for the Haber process and why
- high pressure 2 atmospheres - as very high pressure is expensive and requires special reaction vessels
- low temp 400degrees - rate is highest if its at a high temp
the contact process (making sulfuric acid)
equation & conditions?
2SO2(g) + O2(g) <=> 2SO3(g)
= -197KJ/mol
- 450 degrees temp
- low pressure 1 atmosphere
Making ethanol
C2H4(g) + H2o(g) <=>CH3CH2OH(g)
= -42
what is the formula for the equilibrium law?
aA + bB <=> cC + dD
what does the equilibrium law state?
the direction of an equilibrium is dependant on the conc. of components of the reaction
equilibrium law equation?
Kc = [C]c [D]d / [A]a [B]b
products / reactants
what does K stand for
equilibrium constant
what does Kc stand for
equilibrium constant in terms of concentration
what does [C] or [D] stand for?
what does [A] or [B] stand for?
- equilibrium conc of the products in mol/dm3
- equilibrium conc of the reactants in mol/dm3
what power is each conc raised to in a Kc equation
each conc is raised to the power of its balancing number in the overall equation
units for Kc
change depending on the balancing number
what does the equilibrium constant in terms of conc (Kc) compare?
the conc of reactants and products present at equilibrium ‘how far’ the equilibrium has shifted
what does a large Kc value mean?
the equilibrium position lies to the right hand side of the reaction and favours the product
what does a low Kc value mean?
the equilibrium position lies to the left hand side of the reaction and favours the reactants
what is a ‘central equilibrium’?
(equal con of reactant and products) has Kc = 1
what is the only factor that effects Kc?
temperature
Kc is only constant at a constant temperature
what would an equation have no units
no units, as they cancel out. this is due to there being an equal number of moles on both sides of the equation
