A chemical system can be thought of as being either:

Voiceover Our goal is to calculate the equilibrium constant K for this reaction, so for this reaction right here. Now we're gonna use the standard reduction potentials to do so. So in the previous video, we talked about the relationship between the equilibrium constant K and the standard cell potential.

1.At equilibrium

2.Not at equilibrium

Calculate the concentrations and substitute them into an expression and compute the 'experimental concentration quotient' or 'Q'. If Q is equal to K eq (50 in this case) then the system is already at equilibrium and stable. If Q K eq then the product is too high and must decrease. Therefore the reverse reaction is favoured. In general, to calculate the total energy of a given conformation, add all the torsional and steric strain: For example: Calculate the energy difference between these two conformations of butane: The first conformation has one CH 3 /CH 3 gauche interaction which brings 3.8 kJ/mol energy of destabilization. Equilibrium Constant Calculator is a free online tool that displays the equilibrium constant for the given chemical reaction. BYJU’S online equilibrium constant calculator tool makes the calculation faster, and it displays the result in a fraction of seconds. Mar 14, 2019  The cell potential and free energy example shows how to calculate free energy of a redox reaction. If ΔG = 0:, solve for E cell 0 = -nFE cell E cell = 0 V This means, at equilibrium, the potential of the cell is zero. The reaction progresses forward and backward at the same rate, meaning there is no net electron flow. With no electron flow, there is no current and the potential is equal to zero.

A system which is not at equilibrium will move spontaneously to a position of being at equilibrium.

What is Keq : The 'K' in Keq stands for 'Constant'. The 'eq' means that the reaction is at equilibrium. Very roughly, Keq tells you the ratio of Products/Reactants for a given reaction at equilibrium at a certain temperature.

K eq = [Products] / [Reactants]

Consider the reaction

2HI(g ) < ---------------> H2(g) + I2(g)

that if you take the [H2], the [I2] and the [HI] in an equilibrium mixture of these at 423 °C,the expression

[H 2 ] [I 2 ] / 2 [HI] = 0.0183

this is Keq expression this is value of Keq
Writing Keq Expressions:
Consider the general reaction:
aA + bB <------> cC + dD
where, A,B,C,D denote the reactants and prodcuts and a,b,c,d are coefficients in the balanced chemical equation.The equilibrium-constant expression for a reaction is an expression obtained by multiplying the concentrations of products,dividing by th concentration of reactants and raising each concentration term to a power equal to the coefficent in the chemical equation.
The equilibrium constant Kc is the value obtained for the equilibrium-constant expression when equilibrium concentrations are substituted.
Keq= [C]c [D]d / [A]a [B] b
Here you denote the molar concentration of a substance by writing its formula is square brackets.The subscript eq on the equilibrium contant means that it is defined in terms of molar concentrations.
The Keq Expressions for Solids and Liquids
For solids: When we write the Keq expression for a reaction with solids, we simply leave out the solids.

the Keq expression for the equation:

CaCO3(s) <---------> CaO(s) яАл + CO2(g)

is simply: Keq = [CO2]

Calculate Keq For The Reaction

The same argument that was used for solids can also be used for liquids. Thus, we can expand the last statement:

'When we write the Keq expression for a reaction with solids or liquids, we simply leave out the solids and the liquids'.

Gases and aqueous solutions do undergo changes in concentration so they are always

included in the Keq expression.

Equilibrium Constants

Equilibrium is a state of balance between products and reactants. When the rate of the forward reaction is equal to the rate of the reverse reaction, the concentrations of products and reactants remain constant. Every reaction is striving to reach equilibrium.
Le Chatelier’s Principle : if equilibrium is disturbed (eg. if product or reactant concentrations are altered), the direction of the reaction will shift to restore the state of equilibrium.
Equilibria are reflections of Le Chatelier’s Principle. If we begin a reaction with only the reactants, they will readily form products. As the concentration of the products increases, the rate of the reverse reaction increases. As the concentration of reactants decreases, the rate of the forward reaction decreases. Eventually the reaction rates will cancel each other out, and there will be no net change in the concentration of reagents.
The Equilibrium Constant(Keq) describes the ratio of products to reactants in a state of equilibrium.
How to calculate keq from pka values

Strong acids and bases dissociate with large equilibrium constants.

We use a specific type of equilibrium constant when describing the dissociation reactions of acids and bases. Recall the equation for the dissociation of an acid:
The Keq of this reaction is given by. We call it Ka, the Acid Dissociation Constant
Likewise, the equilibrium constant for a base dissociation is given by Kb, its Base Dissociation Constant.

The Dissociation Constant determines the strength of the Acid or Base

Strong vs weak Acids
Here is a list of many acids along with their Ka values. The top three on the list would be considered strong acids – they will essentially dissociate completely. Most acids are weak, though two weak acids can vary greatly in Ka.
Most important difference between strong and weak acids: once the reaction reaches equilibrium, strong acids will be dominantly in the conjugate base form. Weak acids will exist as a mixture of the original acid and the conjugate base form.
Adobe premiere pro cs6 family keygen. For simplicity, the strength of the acid will often be given as pKa. pKa represents the same information as Ka except its logarithmic scale eliminates the need for exponential notation. This simple equation converts between Ka and pKa.
Using these equations, see how a large pKa denotes a very weak acid. Bases have very large pKa
Bases use Kb and pKb as measurement of how favorably they accept protons (basicity). Kb works exactly like ka. A small Kb means equilibrium highly favors conjugate acid formation, indicating a strong base. A larger Kb indicates a weak base that will partially form conjugate acid and partially remain in its base form.
General Note: A stronger acid or base will produce a weaker conjugate. A weaker acid or base will produce a stronger conjugate.

Summary

Here is an example of an acid base reaction. The Keq is 1.8e-5
Do we start with an acid or a base?
NH3 (ammonia) is a base. This is clear because the products include its protonated form NH4 (ammonium). We see it is acting like a base and accepting a proton from water.
The conjugate acid is ammonium. In the reverse reaction, ammonium acts as an acid and hydroxide acts as a base. Ammonium donates a proton to hydroxide.
Find Kb for ammonia: This would simply be the given Keq for the reaction. Kb is just the Keq of a specific type of reaction between a base and water. Kb = 1.8e-5. Ammonia is a weak base.
Find Ka of conjugate acid. This is would equal the Keq of the reverse reaction. The Keq of the reverse reaction is the reciprocal of the the forward reaction. Ka = 1/Kb = 5.6e-10. Since ammonia is a base of moderate strength (though defined as ‘weak’), see how its conjugate acid is is very very weak. This makes sense because if the conjugate acid were stronger, the reverse reaction would be more favorable, causing the forward base reaction to become less favorable.

How To Calculate Keq Values With Pka

Convert Ka and Kb to pKa and pKb.
pKb = 4.75 pKb = 9.25

How To Calculate Keq In Chemistry

Note: pKa + pKb = 14.0
After reading this you should be able to: