Equilibrium
Chemistry - Equilibrium
What state is reached when forward and reverse reaction rates are equal?
Equilibrium
Explanation: Chemical equilibrium occurs when the rates of the forward and reverse reactions are perfectly equal, resulting in no net change in the concentrations of reactants and products.
What type of reaction can proceed in both forward and reverse directions?
Reversible
Explanation: A reversible reaction is one where products can react to reform the original reactants, typically indicated by a double arrow in chemical equations.
According to Le Chatelier, adding a reactant shifts the equilibrium to which side?
Right
Explanation: Adding a reactant increases its concentration, prompting the system to consume the excess by shifting to the right, favoring product formation.
Removing a product from a system shifts the equilibrium to which side?
Right
Explanation: Removing a product decreases its concentration, so the system shifts to the right to synthesize more of the lost product and restore balance.
Adding a product to a closed system shifts the equilibrium to which side?
Left
Explanation: Introducing extra product increases its concentration, causing the system to shift to the left, consuming the excess product to form reactants.
Removing a reactant from a system shifts the equilibrium to which side?
Left
Explanation: Removing a reactant reduces its concentration, leading the system to shift to the left to replenish the missing reactant from the products.
What physical factor is the only one that alters the value of the equilibrium constant?
Temperature
Explanation: Temperature changes the kinetic energy of the system, fundamentally altering the forward and reverse reaction rates differently, which intrinsically changes the equilibrium constant.
What type of macroscopic system is necessary to establish chemical equilibrium?
Closed
Explanation: A closed system prevents the escape or entry of matter, ensuring all reactants and products remain continuously available to reach a dynamic balance.
What happens to the macroscopic observable properties of a system once it reaches equilibrium?
Stabilize
Explanation: At equilibrium, macroscopic properties like color, pressure, and concentration stabilize and remain constant because the net reaction rate is effectively zero.
What term describes an equilibrium where all reactants and products are in the same phase?
Homogeneous
Explanation: Homogeneous equilibrium occurs when all participating chemical species are in the exact same state of matter, such as all being gases or all aqueous.
What term describes an equilibrium with components present in multiple distinct phases?
Heterogeneous
Explanation: Heterogeneous equilibrium involves reactants and products in two or more different states of matter, such as a solid reacting with a gas.
Which physical state is completely excluded from the calculation of the equilibrium constant?
Solid
Explanation: Pure solids are excluded from the equilibrium expression because their active concentrations (density) remain constant regardless of the actual mass present.
Besides solids, which other pure physical state is omitted from the equilibrium expression?
Liquid
Explanation: Pure liquids, typically acting as solvents in vast excess, have effectively constant concentrations and are thus omitted from the equilibrium constant calculation.
What substance speeds up reaching equilibrium without altering the equilibrium constant itself?
Catalyst
Explanation: A catalyst lowers the activation energy for both the forward and reverse reactions equally, reducing the time required to reach equilibrium without shifting its final position.
In an exothermic reaction, increasing the temperature shifts the equilibrium to which side?
Left
Explanation: An exothermic reaction releases heat as a product. Increasing temperature adds excess heat to the system, shifting equilibrium to the left to consume it.
In an endothermic reaction, increasing the temperature shifts the equilibrium to which side?
Right
Explanation: Endothermic reactions absorb heat as a reactant. Increasing the temperature provides more heat, shifting equilibrium right to form more products.
Decreasing temperature in an exothermic process favors the formation of what?
Products
Explanation: Removing heat from an exothermic reaction pulls the equilibrium to the right, heavily favoring the formation of products in an attempt to generate more heat.
Decreasing temperature in an endothermic process favors the formation of what?
Reactants
Explanation: Removing heat from an endothermic reaction essentially starves it of a necessary reactant, shifting equilibrium left to favor the formation of reactants.
What calculated quantity compares current non-equilibrium concentrations to the equilibrium constant?
Quotient
Explanation: The reaction quotient (Q) uses the exact same mathematical formula as the equilibrium constant (K) but is calculated using current, instantaneous concentrations to predict the reaction direction.
If the reaction quotient is exactly equal to the equilibrium constant, what is the state?
Equilibrium
Explanation: When Q equals K, the current concentrations exactly match the natural equilibrium concentrations, meaning the system is perfectly at equilibrium.
If the reaction quotient is greater than the equilibrium constant, which direction will the reaction shift?
Reverse
Explanation: A Q value greater than K indicates an unnatural excess of products, prompting the system to shift in the reverse direction to consume them.
If the reaction quotient is less than the equilibrium constant, which direction will the reaction shift?
Forward
Explanation: A Q value less than K indicates an excess of reactants relative to products, driving the system to shift forward to produce more products.
What specific variable typically represents the equilibrium constant based on molar concentration?
Kc
Explanation: Kc denotes the specific equilibrium constant derived using the molar concentrations (moles per liter) of the aqueous or gaseous reactants and products.
What specific variable represents the equilibrium constant based on the partial pressures of gases?
Kp
Explanation: Kp represents the specific equilibrium constant calculated explicitly using the equilibrium partial pressures of the gaseous components involved in a reaction.
Increasing pressure on a gaseous system shifts equilibrium toward the side with fewer what?
Moles
Explanation: Increasing pressure forces the system to reduce pressure by shifting toward the side of the balanced chemical equation that has fewer moles of gas.
In a gas equilibrium, an artificial increase in volume decreases what specific physical property?
Pressure
Explanation: According to Boyle's Law, increasing the volume of a closed gaseous system directly decreases its overall pressure, potentially causing an equilibrium shift.
What type of gas addition at constant volume has absolutely no effect on the equilibrium position?
Inert
Explanation: Adding an inert gas (like argon) at constant volume increases total pressure but doesn't change the partial pressures of the reacting gases, thus no shift occurs.
What specific characteristic describes chemical equilibrium at the active molecular level?
Dynamic
Explanation: Chemical equilibrium is considered dynamic because the forward and reverse reactions continue to occur vigorously at the molecular level, just at the exact same rate.
If the equilibrium constant is much greater than one, the mixture consists mostly of what?
Products
Explanation: A large K value (K > 1) signifies that the numerator in the equilibrium expression is larger, meaning products heavily dominate the mixture at equilibrium.
If the equilibrium constant is much less than one, the mixture consists mostly of what?
Reactants
Explanation: A small K value (K < 1) means the denominator is much larger, indicating the equilibrium mixture is composed predominantly of unreacted reactants.
What scientist's principle predicts how an equilibrium system responds to external disturbances?
Chatelier
Explanation: Henri Le Chatelier formulated the principle stating that an equilibrium system will shift to counteract any external disturbance, such as concentration or temperature changes.
What happens mathematically to the equilibrium constant of a chemical reaction if it is reversed?
Inverted
Explanation: Reversing a chemical equation flips the numerator and denominator in its equilibrium expression, making the new constant the mathematical reciprocal (inversion) of the original.
If you multiply a reaction equation's coefficients by two, what happens to the equilibrium constant?
Squared
Explanation: Multiplying stoichiometric coefficients raises the concentration terms in the equilibrium expression to that power, effectively squaring the entire equilibrium constant.
For the Haber process, what long-term effect does a catalyst have on the final equilibrium yield?
None
Explanation: An iron catalyst in the Haber process accelerates the reaction to reach equilibrium faster, but it absolutely does not alter the final yield of ammonia.
In a gaseous equilibrium, adding an inert gas at constant pressure artificially increases what property?
Volume
Explanation: To maintain a constant total pressure when an inert gas is added, the system's volume must expand, which lowers the partial pressures of the reacting gases.
What specific equilibrium constant applies to the dissociation of sparingly soluble ionic compounds?
Ksp
Explanation: The solubility product constant (Ksp) defines the equilibrium between a solid ionic compound and its dissolved ions in a saturated aqueous solution.
What type of ion effect typically decreases the solubility of a sparingly soluble salt in solution?
Common
Explanation: The common ion effect occurs when adding an ion that is already present in the equilibrium shifts the reaction to the left, decreasing the salt's solubility.
What specific constant represents the autoionization product of water at equilibrium?
Kw
Explanation: The ion-product constant for water (Kw) is the product of the equilibrium concentrations of hydrogen and hydroxide ions, equaling 1.0 x 10^-14 at 25°C.
What type of acid completely dissociates in water, meaning the equilibrium lies extremely far right?
Strong
Explanation: Strong acids, like HCl, ionize practically 100% in aqueous solutions; the forward reaction is so complete that the equilibrium is pushed entirely to the products.
What type of acid only partially dissociates, establishing a measurable equilibrium with its respective ions?
Weak
Explanation: Weak acids, like acetic acid, do not ionize completely, thereby creating a measurable dynamic equilibrium between the intact acid molecules and their dissociated ions.
What specific equilibrium constant is used to describe the absolute dissociation extent of a weak acid?
Ka
Explanation: The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution, based on its equilibrium concentrations.
What specific equilibrium constant is used to describe the absolute dissociation extent of a weak base?
Kb
Explanation: The base dissociation constant (Kb) evaluates the strength of a weak base by measuring the equilibrium ratio of its conjugate acid and hydroxide ions.
If a reaction equation is halved, what mathematical operation is logically applied to its equilibrium constant?
Root
Explanation: Multiplying an equation by a factor of 1/2 corresponds to raising the equilibrium constant to the power of 1/2, which is mathematically equivalent to taking its square root.
When two distinct equilibrium reactions are added together, what is done to their respective equilibrium constants?
Multiplied
Explanation: When adding sequential reaction steps to get an overall reaction equation, the equilibrium constant for the overall reaction is the mathematical product of the individual constants.
For the reaction A(g) becoming 2B(g), increasing the total system pressure shifts the equilibrium to which side?
Left
Explanation: This reaction produces 2 moles of gas from 1 mole. Increasing pressure shifts equilibrium to the left toward the reactant to reduce the total number of gaseous moles.
For the reaction A(s) becoming B(g), what is the exact effect of adding more solid A on the equilibrium position?
None
Explanation: The concentration of a pure solid is constant and does not appear in the equilibrium expression, so adding more solid has absolutely no effect on the equilibrium position.
In the classic reaction of nitrogen and hydrogen to form ammonia, what is the physical phase of all components?
Gas
Explanation: The Haber process is a classic example of a homogeneous equilibrium where nitrogen, hydrogen, and the resulting ammonia are all entirely in the gaseous phase.
What type of substance classically acts as a proton donor in an aqueous acid-base equilibrium system?
Acid
Explanation: According to the Brønsted-Lowry theory, an acid is fundamentally defined as any substance that can donate a proton (H+) to another substance in an equilibrium reaction.
What term describes a solution containing a weak acid and its conjugate base that strongly resists pH changes?
Buffer
Explanation: A buffer solution utilizes the common ion effect to absorb small amounts of added acid or base, thereby maintaining a relatively constant pH in the system.
In a buffer system, what famous equation mathematically relates the pH to the equilibrium constant and species concentrations?
Henderson
Explanation: The Henderson-Hasselbalch equation simplifies buffer pH calculations by directly relating the pH to the pKa and the logarithm of the ratio of conjugate base to acid.
When the reaction quotient is calculated using initial partial pressures instead of exact concentrations, what is it called?
Qp
Explanation: Qp is the specific reaction quotient calculated using the momentary partial pressures of reacting gases, directly mirroring the format of the Kp expression.
What exact process describes the formation of a solid from a solution when the ion product Qsp strictly exceeds Ksp?
Precipitation
Explanation: When Qsp > Ksp, the solution is supersaturated, and the system shifts left to establish equilibrium by dropping the excess ions out of solution as a solid precipitate.
If the calculated equilibrium constant exactly equals one, what is the standard free energy change of the reaction?
Zero
Explanation: The thermodynamic relationship ΔG° = -RT ln(K) means that when K=1, the natural log of K is exactly 0, resulting in a standard free energy change of strictly zero.
What specific thermodynamic potential is strictly minimized when a chemical system reaches equilibrium at constant temperature and pressure?
Gibbs
Explanation: The Gibbs free energy (G) naturally decreases as a reaction proceeds towards equilibrium; at the exact point of equilibrium, it reaches its absolute minimum possible value.
In a closed liquid-vapor equilibrium system, what specific measurable physical property remains constant at a given temperature?
Pressure
Explanation: In a sealed container at constant temperature, the rates of evaporation and condensation equalize, establishing a perfectly constant equilibrium vapor pressure.
What happens to the active bulk concentration of a pure solid during a chemical reaction strictly at equilibrium?
Constant
Explanation: Because a solid's density does not change, its active bulk concentration remains completely fixed and constant, which is why it is excluded from equilibrium equations.
In a standard equilibrium graph of substance concentration versus time, what geometric shape do the component lines eventually become?
Horizontal
Explanation: On a concentration-time graph, the point where equilibrium is achieved is visually marked by the concentration lines flattening out and becoming perfectly horizontal.
What happens to the absolute active rates of both the forward and reverse reactions when a suitable catalyst is added?
Increase
Explanation: A catalyst lowers the activation energy barrier for the entire process, causing both the forward and the reverse reaction rates to increase equally.
For a gaseous reaction where the total change in moles is exactly zero, what is the mathematical relationship between Kp and Kc?
Equal
Explanation: The formula Kp = Kc(RT)^Δn links the constants. If the change in moles of gas (Δn) is zero, (RT)^0 equals 1, making Kp perfectly equal to Kc.
If the equilibrium constant steadily increases when the system's absolute temperature increases, what thermodynamic type of reaction is it?
Endothermic
Explanation: An increasing K with higher temperature means products are favored. This directly matches Le Chatelier's principle for an endothermic reaction absorbing the added heat.
