Chapter 15: Chemical Equilibrium Flashcards
(32 cards)
What does K measure?
The value of K is a measure of how far a reaction proceeds–the larger the value of K, the moe the reaction proceeds towards the products.
What is the dynamic equilibrium for a chemical reaction?
The condition in which the rate of the forward reaction equals the rate of the reverse reaction.
How is the equilibrium constant (K) defined?
K is defined for a reaction as the ratio–at equilibrium–of the concentrations of the produces raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients.
What is the law of mass action?
The relationship between the balanced chemical equation and the expression of the equilibrium constant.
If the equation is reversed, what happens to the equilibrium constant?
It is inverted.
If we multiply the coefficients in the equation by a factor, what happens to the equilibrium constant?
We raise the equilibrium constant to the same factor.
If we add two or more individual chemical equations to obtain an overall equation, what happens to the equilibrium constants?
We multiply the corresponding equilibrium constants by each other to obtain the overall equilibrium constant.
What is Kc?
The equilibrium constant with respect to concentration in molarity.
What is Kp?
The equilibrium constant with respect to partial pressures in atmospheres.
How is the expression for Kp related to the expression for Kc?
The expression for Kp takes the form of the expression for Kc, except that we use the partial pressure of each gas in place of its concentration.
Are Kp and Kc equal? Why?
Because the partial pressure of a gas in atm in not the same as its concentration in molarity, the value of Kp for a reaction is not necessarily equal to the value of Kc. However, as long the gases are behaving ideally, we can derive a relationship between the two constants.
Give the expression that relates Kp to Kc.
Kp = Kc(RT)^∆n
What is the reaction quotient?
The ratio–at any point in the reaction–of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients.
What is the difference between K and Q?
At a given T, K has only one value and it specifies the relative amounts of reactants and products at equilibrium. Q, by contrast, depends on the current state of the reaction and has many different values as the reaction proceeds.
Why is the reaction quotient (Q) useful?
The value of Q relative to K is a measure of the progress of the reaction toward equilibrium.
When is Q equal to K?
At equilibrium.
How will Q change when it is less than K?
It must get larger as the reaction proceeds toward equilibrium. Q becomes larger as the reactant concentration decreases and the product concentration increases–the reaction proceeds to the right.
How will Q change when it is greater than K?
It must get smaller as the reaction proceeds toward equilibrium. Q becomes smaller as the reactant concentration increases and the product concentration decreases–the reaction proceeds to the left.
How do you check the validity of the x is small approximation?
By comparing the calculated value of x to the number from which it was subtracted. The ratio of x to the number it is subtracted from should be less than 0.05 for the approximation to be valid.
What is Le Chatlier’s principle?
When a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance.
What happens when the concentration of a reactant is lowered?
Lowing the concentration of a reactant (which makes Q > K) causes the system to shift in the direction of the reactants to minimize the disturbance.
What happens when the concentration of a product is lowered?
Lowering the concentration of a product (which makes Q < K) causes the system to shift in the direction of products.
What effect does decreasing the volume of a reaction have?
Decreasing the volume causes the reaction to shift in the direction that has the fewer moles of gas particles.
What effect does increasing the volume of a reaction have?
Increasing the volume causes the reaction to shift in the direction that has the greater number of moles of gas particles.
