Questions and Answers 2026.
Dynamic Equilibrium - Answer For a chemical reaction, the condition in which the rate of the
forward reaction equals the rate of the reverse reaction.
Equilibrium Constant (K) - Answer The ratio (at equilibrium) of the concentrations of the
products raised to their stoichiometric coefficients divided by the concentrations of the
reactants raised to their stoichiometric coefficients.
aA+bB↔cC+dD
K=([C]^c[D]^d)/([A]^a[B]^b)=[products]/[reactants]
Relative Size of Keq - Answer If K>>1, reaction proceeds forward; favors products
If K<<1, reaction proceeds a little; favors reactants
If K≈1, reaction proceeds about half way
Relationships Between Keq and the Chemical Equation - Answer If the reaction is reversed:
Kreverse = 1/Kforward
If the coefficients in the equation are multiplied by a factor: raise the equilibrium constant to
the same factor
If two or more individual chemical equations are added: multiply the corresponding equilibrium
constants by each other to obtain the overall Keq
Heterogeneous Equilibria Involving Solids and Liquids - Answer The concentrations of pure
liquids and solids remain constant and are therefore excluded from the equilibrium expression.
Expressing Keq in Terms of Pressure - Answer Kp=Kc(RT)^(∆n)
where Kp is the equilibrium constant with respect to partial pressures in atm, Kc is the
equilibrium constant with respect to concentration, R=0.08206 L·atm/mol·K, T is temperature in
K, and ∆n is the change in number of moles of gas
Reaction Quotient (Qc) - Answer the ratio (at any point in the reaction) of the concentrations
of the products raised to their stoichiometric coefficients divided by the concentrations of the
reactants raised to their stoichiometric coefficients.
, Q, K, and the Direction of a Reaction - Answer If Q<K, reaction goes forward (toward
products)
If Q=K, reaction is at equilibrium
If Q>K, reaction goes backwards (toward reactants)
Le Châtelier's Principle - Answer When a chemical system at equilibrium is disturbed, the
system shifts in a direction that minimizes the disturbance.
Summary of Le Châtelier's Principle: Changes in Pressure - Answer Decreasing the volume
causes the reaction to shift in the direction that has the fewer moles of gas particles.
Increasing the volume cases the reaction to shift in the direction that has the greater number of
moles of gas particles.
If a reaction has an equal number of moles of both sides of the chemical equation, then a
change in volume produces no effect on the equilibrium.
Adding an inert gas to the mixture at a fixed volume has no effect on the equilibrium.
Summary of Le Châtelier's Principle: Changes in Concentration - Answer Increasing the
concentration of one or more of the reactants (which makes Q<K) causes the reaction to shift in
the direction of the products.
Increasing the concentration of one or more of the products (which makes Q>K) causes the
reaction to shift in the direction of the reactants.
Decreasing the concentration of one or more of the reactants (which makes Q>K) causes the
reaction to shift in the direction of the reactants.
Decreasing the concentration of one or more of the products (which makes Q<K) causes the
reaction to shift in the direction of the products.
Summary of Le Châtelier's Principle: Changes in Temperature - Answer In an exothermic
reaction:
Increasing the temperature causes an exothermic reaction to shift in the direction of the
reactants; the value of Keq decreases.
Decreasing the temperature causes an exothermic reaction to shift in the direction of the
products; the value of Keq increases.
In an endothermic reaction:
Increasing the temperature causes an endothermic reaction to shift in the direction of the
products; the value of Keq increases.
Decreasing the temperature causes an endothermic reaction to shift in the direction of the
reactants; the value of Keq decreases.