Which statement best describes a system at dynamic equilibrium?
The forward and reverse reactions occur at equal rates and concentrations remain constant.
All chemical reactions have completely stopped.
The concentrations of reactants equal the concentrations of products.
Only the forward reaction is still occurring.
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WhyAt dynamic equilibrium the forward and reverse reactions continue at equal rates, so concentrations of reactants and products stay constant over time.
2Multiple choice · Easy
For the reaction N2(g) + 3 H2(g) <=> 2 NH3(g), what is the correct expression for Kc?
[NH3]^2 / ([N2][H2]^3)
[N2][H2]^3 / [NH3]^2
[NH3]^2 / ([N2][H2])
2[NH3] / ([N2] + 3[H2])
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WhyKc places product concentrations over reactant concentrations, each raised to its stoichiometric coefficient: [NH3]^2 / ([N2][H2]^3).
3Multiple choice · Easy
A reaction has a very large equilibrium constant (K >> 1). This indicates that at equilibrium the system contains:
mostly products
mostly reactants
equal amounts of reactants and products
no reactants or products
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WhyA large K means the numerator (products) greatly exceeds the denominator (reactants), so products are strongly favored at equilibrium.
4Multiple choice · Easy
According to Le Chatelier's principle, adding more reactant to a system at equilibrium will cause the equilibrium to shift:
toward the products
toward the reactants
in neither direction
so that K decreases
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WhyAdding reactant increases its concentration, so the system shifts toward the products to consume the added reactant and re-establish equilibrium.
5Fill in the blank · Easy
The equilibrium constant expressed in terms of partial pressures of gases is given the symbol .
Answer:
Kp
WhyKp is the equilibrium constant written using partial pressures of gaseous species instead of molar concentrations.
6Fill in the blank · Easy
For a solid dissolving in water such as AgCl(s) <=> Ag+(aq) + Cl-(aq), the equilibrium constant for dissolution is called the solubility product constant, symbol .
Answer:
Ksp
WhyKsp is the solubility product constant, the equilibrium constant for a slightly soluble salt dissolving into its ions.
7Multiple choice · Medium
For the reaction 2 SO2(g) + O2(g) <=> 2 SO3(g), the reaction quotient Q is found to be greater than K. Which way will the reaction proceed to reach equilibrium?
in the reverse direction, forming more reactants
in the forward direction, forming more products
it is already at equilibrium and will not shift
it cannot be determined without temperature
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WhyWhen Q > K there are too many products relative to equilibrium, so the net reaction proceeds in the reverse direction toward reactants.
8Multiple choice · Medium
For the equilibrium H2(g) + I2(g) <=> 2 HI(g), the equilibrium concentrations are [H2] = 0.20 M, [I2] = 0.20 M, and [HI] = 1.6 M. What is the value of Kc?
Chemical equilibrium: The state in which the forward and reverse reaction rates are equal, so the concentrations of reactants and products no longer change over time.
Dynamic equilibrium: An equilibrium in which both forward and reverse reactions continue at equal rates rather than stopping, keeping macroscopic concentrations constant.
Reversible reaction: A reaction that can proceed in both the forward and reverse directions, written with a double arrow (<=>).
Forward reaction: The conversion of reactants into products as written from left to right in a chemical equation.
Reverse reaction: The conversion of products back into reactants, proceeding from right to left.
Equilibrium constant (K): A number expressing the ratio of product to reactant activities at equilibrium, each raised to its stoichiometric coefficient.
Law of mass action: The principle that the equilibrium expression is the product concentrations over the reactant concentrations, each raised to its coefficient.
Equilibrium expression: The mathematical formula relating reactant and product amounts that equals K at equilibrium.