Chapter 15 - Chemical Equilibrium Flashcards
*Understand what's meant by chemical equilibrium & how it relates to reaction rates *Write the equilibrium-constant expression for any rate *Relate Kc & Kp *Relate the magnitude of an equilibrium constant to the relative amounts of reactants & products present in an equilibrium mixture *Manipulate the equilibrium constant to reflect changes in the chemical equation *Write the equilibrium-constant expression for a heterogeneous reaction *Calculate an equilibrium constant from concentration
Define “chemical equilibrium”.
Occurs when opposing reactions are proceeding at equal rates.
15.1 How are reversible reactions represented?
By one arrow going right, and one arrow going left
15.1 When a system reaches equilibrium, what happens to the concentrations?
They no longer change.
15.1 For equilibrium to occur, neither reactants nor products can…
Escape from the system
15.1 At equilibrium, what equals a constant?
A particular ratio of concentration terms Ex. Kf — = constant Kr
15.1 - Give It Some Thought (p. 630) A. Which quantities are equal in a dynamic equilibrium? kf[N2O4] = kr[NO2]^2 B. If the rate constant for the forward reaction (k[N2O4]) is larger than the rate constant for the reverse reaction k[NO2[, will the constant be greater than or equal to 1?
A. The rates of opposing reactions B. Larger than 1.
15.2 Haber Process
N2(g) + 3H2(g) (back & forth arrows) 2 NH3(g)
15.2 - Give It Some Thought (p. 630) 15.2 How do we know when equilibrium has been reached in a chemical reaction?
The reaction appears to stop.
15.2 Law of Mass Action
For any reaction, the relationship between the concentrations of the reactants & products present at equilibrium. a A + b B (back & forth arrows) d D + e E LoMA: Kc = [D]^d[E]^e / [A]^a[B]^b
15.2 Define “equilibrium constant”.
Kc. The numerical value obtained when we substitute equilibrium concentrations into the equilibrium-constant expression. C indicates that concentrations expressed in molarity are used to evaluate the constant.
15.2 The equilibrium-constant expression depends only on…
the stoichiometry of the reaction, not the mechanism.
15.2 How does the value of Kc depend on the starting concentrations?
It doesn’t.
15.2 - Give It Some Thought (p. 633) What do the symbols Kc and Kp represent?
Equilibrium constants. Kc is based on molarity, Kp is based on partial pressures (in atm).
15.2 The activity of any substance in an ideal mixture is…
the ratio of the concentration or pressure of the substance to a reference concentration (1 M) or a reference pressure (1 atm).
15.2 - Give It Some Thought (p. 635) If the concentration of N2O4 in an equilibrium mixture is 0.00140 M, what is its activity? (Assume the solution is ideal).
0.00140 M/1 M = 0.00140
