Equilibrium Flashcards
equilibrium (2)
When the rate of the forward reaction equals the rate of the reverse reaction, the concentrations of the reactant and product species remain constant over time
What slows the slows the forward reaction rate?
The decreasing concentration of the reactant
what speeds the reverse reaction rate?
the increasing product concentration
Reaction Quotient
+how is it derived
Tells us if reaction is at equilibrium or not
the reaction quotient is derived directly from the stoichiometry of the balanced equation as
Reaction quotient when products and reactants are gases
a reaction quotient may be similarly derived using partial pressures:
as a reaction proceeds towards equilibrium what varies?
Explain how it does
The numerical value of Q varies
As the reaction proceeds toward equilibrium in the forward direction, reactant concentrations decrease (as does the denominator of Qc), product concentration increases (as does the numerator of Qc), and the reaction quotient consequently increases. When equilibrium is achieved, the concentrations of reactants and product remain constant, as does the value of Qc.
If the reaction begins with only product present……
Qc+what happens
the value of Qc is initially undefined (immeasurably large, or infinite):
In this case, the reaction proceeds toward equilibrium in the reverse direction. The product concentration and the numerator of Qc decrease with time, the reactant concentrations and the denominator of Qc increase, and the reaction quotient consequently decreases until it becomes constant at equilibrium.
equilibrium constant, K
The constant value of Q exhibited by a system at equilibrium
law of mass action
At a given temperature, the reaction quotient for a system at equilibrium is constant. aka Equilibrium constants are constant at constant temperature
A reaction exhibiting a large K indicates that it….
most of the reactant has been converted to product
a small K indicates the reaction achieves equilibrium after
very little reactant has been converted
A homogeneous equilibrium
all reactants and products (and any catalysts, if applicable) are present in the same phase.
Water and reaction quotient
Why? What only does it RQ include?
Water is not included in the reaction quotient because its conctration cannot be increased. It is already pure.
reaction quotients include concentration or pressure terms only for gaseous and solute species.
And so, the relationship between Kc and KP is
heterogeneous equilibrium
involves reactants and products in two or more different phases,
How to find Kp with Kc
kp=kc (RT)^n
n is the order so remember product-reactant stoich coefficient wise
so what does an equilibrium reaction not include? write me the reaction kc/kp for this question then:
pure liquids and solids
coupled equilibria
coupled equilibria involve two or more separate chemical reactions that share one or more reactants or products.
equilibrium constant for the reversed equation is
simply the reciprocal of that for the forward equation.
Changing the stoichiometric coefficients in an equation by some factor x results in
an exponential change in the equilibrium constant by that same factor:
Adding two or more equilibrium equations together yields
an overall equation whose equilibrium constant is the mathematical product of the individual reaction’s K values:
How to find overall reaction Kc when given the elementrary equations plus elementary kc? (3)
- see if the reverse elementary step Kc have to be reversed or not. depending if products/reactants of the overall equation are on which side
- see if you need to exponentially increase elemnetary Kc, (kc)^x based on elementary coefficients and overal equation coefficient
- multiply the modified elementary coefficient all tgt
If an equilibrium system is subjected to a change in conditions that affects these reaction rates (forward and reverse reactions taking place at equal rates) differently (a stress), then
talk about what the rate now is and what will happen
the rates are no longer equal and the system is not at equilibrium. The system will subsequently experience a net reaction in the direction of greater rate (a shift) that will re-establish the equilibrium.
Le Châtelier’s principle
if an equilibrium system is stressed, the system will experience a shift in response to the stress that re-establishes equilibrium.
the two stresses that can shift an equilibrium
concentration and temperature
What will happen to the rate at equilibrium if the system is stressed by adding reactant *In terms of forward/reverse
the resulting increase in concentration causes the rate of the forward reaction to increase, exceeding that of the reverse reaction:
in gas equilibrium changes in the partial pressures of any reactant or product are essentially changes in
because…..
concentrations and thus yield the same effects on equilibria
because the partial pressure P of an ideal gas is proportional to its molar concentration M,
how to change pressure/concentration of gas phase equlilibrium? (2)
changing the volume occupied by the system in gas phase the pressures (concentrations) of species in a gas-phase equilibrium can also be changed
adding or removing reactant or product
What are the effects of changing the volume occupied by the system for gas equilibrium? (2)
effect on both end of the arrow+general explanation if volume is changed
Since all species of a gas-phase equilibrium occupy the same volume, a given change in volume will cause the same change in concentration for both reactants and products.
By increasing the volume containing a gas phase reaction at equilibrium, we reduce the partial pressures of all gases present and thus reduce the total pressure. Recall that the response of the synthesis of ammonia to the volume increase was to create more of the reactants at the expense of the products. One consequence of this shift is that more gas molecules are created, and this increases the total pressure in the reaction flask. Thus, the reaction responds to the stress of the volume increase by partially offsetting the pressure decrease with an increase in the number of moles of gas at equilibrium.
What is the relationship between the stoichiometry of a gas-phase equilibrium and the effect of a volume-induced pressure (concentration) change? Explain through example
If the total molar amounts of reactants and products are equal, a change in volume does not shift the equilibrium. If the molar amounts of reactants and products are different, a change in volume will shift the equilibrium in a direction that better “accommodates” the volume change.
What factor stresses changes the equilibrium constant?
temperature
-The equilibrium constant is seen to be a mathematical function of the rate constants for the forward and reverse reactions. Since the rate constants vary with temperature as described by the Arrhenius equation, is stands to reason that the equilibrium constant will likewise vary with temperature (assuming the rate constants are affected to different extents by the temperature change).
What factor stresses does not change the equilibrium constant? (3)
+why? And for. talk abt molecules, for. talk abt the forward and reverse
Reactant/product concentration
pressure
-That means that if you increase the pressure, the position of equilibrium will move in such a way as to decrease the pressure again - if that is possible. It can do this by favoring the reaction which produces the fewer molecules. If there are the same number of molecules on each side of the equation, then a change of pressure makes no difference to the position of equilibrium.
catalyst
-The lowered transition state energy of the catalyzed reaction results in lowered activation energies for both the forward and the reverse reactions. Consequently, both forward and reverse reactions are accelerated, and equilibrium is achieved more quickly but without a change in the equilibrium constant.
In this reaction, aising the temperature of the system is akin to _____, and so the equilibrium will_____
increasing the amount of a reactant
will shift to the right
