Chemistry Ch. 15
In the reversible reaction A--->B, the rate constant of the forward reaction at a particular temperature is 3.0 times the value of the rate constant of the reverse reaction. What is the value of the equilibrium constant at that temperature?
3.0
What is the difference between an equilibrium constant expression and a mass action expression?
An equilibrium constant expression can be used on concentrations of products and reactants in reaction mixtures that have reached equilibrium. Mass action expressions can be used on those reaction mixtures and ones that are on their way to equilibrium (but not actually there)
Mass action expression
Equivalent to the equilibrium constant expression, but applied to reaction mixtures that may, or may not, be at equilibrium.
K for an equation multiplied by a number
If the balanced chemical equation of a reaction is multiplied by some factor n, then the value of K is raised to the nth power.
What is Kc? What is Kp?
Kc is the equilibrium constant based on concentration. Kp is the equilibrium constant based on partial pressure is the substances are gases.
Equation to convert between Kp and Kc
Kp=Kc(RT)^(delta (n)) - Where R=0.0826 ((LxAtm)/molxk)
How can you calculate Kreverse (the equilibrium reaction for the reverse reaction) without recalculating?
Kreverse=1/Kforward
Can the equilibrium constant tell us how fast a reaction reaches equilibrium?
No, it can only tell us the extent of the reaction once equilibrium is reached. (Since is it the ratio of concentrations)
Does the composition of a reaction effect the direction a reaction proceeds to reach equilibrium?
No, they are independent of each other
Are Kc and Kp always the same for a given reaction?
No, they may differ.
What is delta n in the equation to convert between Kp and Kc?
The change in the number of moles of gases. (c+d)-(a+b) - Where c and d are the number of moles of the products and b and d are the number of moles of the reactants.
What does it mean if K is very small? (K<<1)
The concentration of products at equilibrium are much smaller than the concentrations of reactants.
What does it mean if K is very large? (K>>1)
The concentration of products in a reaction mixture at equilibrium are much larger than the concentration of the reactants.
Chemical Equilibrium
The dynamic process in which the concentrations of reactants and products remain constant over time and the rate of a reaction in the forward direction matches its rate in the reverse direction.
Reaction Quotient (Q)
The numerical value of the mass action expression for any values of the concentrations (or partial pressures) of reactants and products; at equilibrium, Q=K
Combining K values
The overall equilibrium constant for a sum of two or more reactions is the product of the equilibrium constants of the individual reactions. K(overall)= K1xK2xK3.....xKn
Law of Mass action
The ratio of the concentrations or partial pressures of products to reactants at equilibrium has a characteristic value at a given temperature when each term is raised to a power equal to the coefficient of that substance in the balanced chemical equation for the reaction.
Equilibrium constant expression
The ratio of the equilibrium concentrations or partial pressures of products to reactants, each term raised to a power equal to the coefficient of that substance in the balanced chemical equation for the reaction.
What does it mean if Q<K?
The reaction as written proceeds in forward direction. There is a net conversion of reactants into products.
What does it mean if Q>K?
The reaction as written proceeds in the reverse direction. There is a net conversion of products into reactants.
Equilibrium Constant (K)
The value of the ratio of concentration (or partial pressure) terms in the equilibrium constant expression at a specific temperature. (Kf/Kr)
Setting up an equilibrium constant
[Concentration of products raised to their coefficient in the balanced chemical equation]/[Concentration on reactants raised to their coefficient in the balanced chemical equation]