What does the reaction quotient $Q$ describe?

The current composition of a reaction mixture, expressed as a ratio of product and reactant terms.

How is $Q_c$ written for $mA+nB\rightleftharpoons xC+yD$?

$Q_c=\frac{[C]^x[D]^y}{[A]^m[B]^n}$; coefficients become exponents.

How does $Q_p$ differ from $Q_c$?

$Q_p$ uses gaseous partial pressures instead of concentrations, with the same product-over-reactant pattern.

How are $Q$ and $K$ related at equilibrium?

They are equal: $Q=K$. At a given temperature, $K$ is independent of the starting mixture.

What does the magnitude of $K$ indicate?

Whether products or reactants are favored at equilibrium; it does not indicate how quickly equilibrium is reached.

General chemistryLesson 2 of 4 in the course Fundamental Equilibrium Concepts

Chemical Equilibrium: Quotients, Phases, and Constant Relationships

5 flashcards · 5 quiz questions · 5 match pairs · 4 fill-in sentences · English

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Summary

This lesson introduces the reaction quotient, $Q$ , a way to describe the current composition of a reversible reaction mixture. Comparing $Q$ with its value at equilibrium helps explain how a reaction changes as it approaches equilibrium.

the concentration-based reaction quotient is

For example, for $2SO_2(g)+O_2(g)\rightleftharpoons2SO_3(g)$ ,

The coefficients become exponents; they are not multiplied by the concentrations.

All flashcards

What does the reaction quotient $Q$ describe?: The current composition of a reaction mixture, expressed as a ratio of product and reactant terms.
How is $Q_c$ written for $mA+nB\rightleftharpoons xC+yD$ ?: $Q_c=\frac{[C]^x[D]^y}{[A]^m[B]^n}$ ; coefficients become exponents.
How does $Q_p$ differ from $Q_c$ ?: $Q_p$ uses gaseous partial pressures instead of concentrations, with the same product-over-reactant pattern.
How are $Q$ and $K$ related at equilibrium?: They are equal: $Q=K$ . At a given temperature, $K$ is independent of the starting mixture.
What does the magnitude of $K$ indicate?: Whether products or reactants are favored at equilibrium; it does not indicate how quickly equilibrium is reached.

Quiz questions

For a reaction mixture with $Q>K$ , which net change moves the system toward equilibrium?Answer: The reverse reaction forms more reactants.
What does a large equilibrium constant generally indicate?Answer: Products are favored in the equilibrium composition.
When adjusted equilibrium equations are added, how is the net equilibrium constant found?Answer: Multiply the adjusted equilibrium constants.
What defines a homogeneous equilibrium system?Answer: All reactants and products are in the same phase.
If every coefficient in a reaction is multiplied by $x$ , how does its equilibrium constant change?Answer: The new constant is the original constant raised to $x$ .

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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