Introduction

Chemical equilibrium is a dynamic state where forward and reverse reactions occur at equal rates. Understanding how systems approach equilibrium and respond to temperature changes is crucial for predicting and controlling chemical reactions.

The Reaction Quotient (Q)

The reaction quotient (Q) helps determine whether a chemical system will proceed toward products or reactants to reach equilibrium. For a general reaction:

$aA + bB \rightleftharpoons cC + dD$

The reaction quotient is expressed as:

$Q = \frac{[C]^c[D]^d}{[A]^a[B]^b}$

Comparing Q and Keq

Temperature Effects on Equilibrium

Endothermic Reactions (ΔH > 0)

For an endothermic reaction:

$A(g) + B(g) \rightleftharpoons AB(g) \quad \Delta H > 0$

The equilibrium constant is:

$K_{eq} = \frac{[AB]}{[A][B]}$

When temperature increases:

Consider the equilibrium shifts:

Species	Initial	Change	Equilibrium
A(g)	[A]	-x	[A] - x
B(g)	[B]	-x	[B] - x
AB(g)	[AB]	+x	[AB] + x

Exothermic Reactions (ΔH < 0)

For an exothermic reaction:

$A(g) + B(g) \rightleftharpoons AB(g) \quad \Delta H < 0$

When temperature increases:

Key Points to Remember