Understanding reversible reactions and dynamic equilibrium states.
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Which of the following statements best defines dynamic equilibrium in a chemical reaction?
The rate of the forward reaction is equal to the rate of the reverse reaction.
At dynamic equilibrium, the reaction continues to occur in both directions, but the rates of the forward and reverse reactions are equal (Rfwd=Rrev), resulting in constant concentrations.
Consider the reversible reaction: N2O4(g)⇌2NO2(g) At equilibrium, which quantity remains constant with time?
The concentrations of both N2O4 and NO2
Once a system reaches equilibrium, the concentrations of all reactants and products remain constant over time, although they are not necessarily equal.
Which of the following conditions is not necessary for a system to reach chemical equilibrium?
The initial concentrations of reactants must be equal to the initial concentrations of products.
Equilibrium can be approached from any starting concentrations. It is not required that initial concentrations be equal.
Graphically, how is the state of equilibrium identified in a Concentration vs. Time plot?
When the reactant and product curves become horizontal (slope = 0).
When the curves become horizontal, the concentrations are no longer changing, indicating the rates of forward and reverse reactions are equal.
Why are radioactive isotopes often used to demonstrate the dynamic nature of chemical equilibrium?
Mixing a radioactive product into an equilibrium mixture results in radioactive reactants over time, proving the reverse reaction is occurring.
If a radioactive isotope is introduced to an equilibrated system, it distributes between reactants and products, proving that the molecular interchange (forward and reverse reactions) continues despite constant macroscopic concentrations.
Write the equilibrium constant expression (Kc) for the following heterogeneous reaction:\nCaCO3(s)⇌CaO(s)+CO2(g)
Kc=[CO2]
The concentrations of pure solids and pure liquids are constant and are omitted from the equilibrium expression. Thus, Kc=[CO2].
For the reaction 2SO2(g)+O2(g)⇌2SO3(g), what is the relationship between Kp and Kc?
Kp=Kc(RT)−1
The relationship is Kp=Kc(RT)Δng. Here, Δng=(moles product gas)−(moles reactant gas)=2−(2+1)=−1. Therefore, Kp=Kc(RT)−1.
If the equilibrium constant for A⇌B is K1=2, what is the equilibrium constant for the reaction 2B⇌2A?
0.25
Reversing the reaction inverts K (1/K1=1/2). Multiplying coefficients by 2 raises the new constant to the power of 2. New K=(1/2)2=1/4=0.25.
Calculate Kc for the reaction 2NO(g)⇌N2(g)+O2(g) given the equilibrium concentrations: [NO]=0.2M, [N2]=0.1M, and [O2]=0.1M.
0.25
Kc=[NO]2[N2][O2]=(0.2)2(0.1)(0.1)=0.040.01=0.25
Which statement about the value of the equilibrium constant K is true?
A large K (K≫1) indicates that products are favored at equilibrium.
If K is very large, the numerator (products) is much larger than the denominator (reactants), meaning the equilibrium favors the products.
