physcial II (p1&2) Flashcards
What does a negative Gibbs Free Energy (ΔG) indicate?
A negative change in Gibbs Free Energy (ΔG<0) indicates that the reaction is spontaneous under the given conditions.
What happens to the Gibbs Free Energy if both enthalpy (ΔH) and entropy (ΔS) are positive?
If both ΔH and ΔS are positive, the reaction will be spontaneous at high temperatures, because the TΔS term (which is positive) will outweigh the positive ΔH term.
What is Gibbs Free Energy?
Gibbs Free Energy (G) is a thermodynamic quantity that combines enthalpy (H), temperature (T), and entropy (S) to predict the spontaneity of a reaction. The formula is:
G=ΔH−TΔS
What does a positive Gibbs Free Energy (ΔG) indicate?
indicates that the reaction is non-spontaneous under the given conditions.
What is the relationship between Gibbs Free Energy and spontaneity?
The spontaneity of a reaction is determined by the sign of the Gibbs Free Energy change (ΔG):
* ΔG<0: Spontaneous reaction.
* ΔG>0: Non-spontaneous reaction.
* ΔG=0: Reaction is at equilibrium.
What is the relationship between Gibbs Free Energy equation and the equilibrium constant (K)
The standard Gibbs Free Energy change (ΔG) is related to the equilibrium constant (K) by the equation:
ΔG=−RTlnK
R is the gas constant with a value of 8.314 J K-1mol-1.
T is the temperature of the reaction in Kelvin
What does it mean if the equilibrium constant (K) is greater than 1 in terms of Gibbs Free Energy?
If the equilibrium constant (K>1), the reaction is product-favored, and ΔG is negative, meaning the reaction is spontaneous under standard conditions.
What does it mean if the equilibrium constant (K) is less than 1 in terms of Gibbs Free Energy?
: If the equilibrium constant (K<1), the reaction is reactant-favored, and ΔG is positive, meaning the reaction is non-spontaneous under standard conditions.
How does temperature affect the spontaneity of a reaction in relation to Gibbs Free Energy?
Temperature affects the spontaneity of a reaction because it influences the entropy term (TΔS) in the Gibbs Free Energy equation.
For a reaction to be spontaneous at high temperatures, -TΔS must be positive, and at low temperatures, ΔH must be negative.
What happens to the Gibbs Free Energy if both enthalpy (ΔH) and entropy (-TΔS) are negative?
If both ΔH and -TΔS are negative, the spontaneity of the reaction depends on the temperature:
* At low temperatures the reaction may be spontaneous.
* At high temperatures the reaction may be non-spontaneous.
What is an acid according to the Arrhenius definition?
An acid is a substance that increases the concentration of hydrogen ions (H⁺) or protons in aqueous solutions
What is a base according to the Arrhenius definition?
A base is a substance that increases the concentration of hydroxide ions (OH⁻) in aqueous solutions.
What is the Bronsted-Lowry definition of an acid
A Bronsted-Lowry base is a proton (H⁺) acceptor.
What is the pH scale?
The pH scale measures the acidity or alkalinity of a solution. It is a scale from 0 to 14, where pH 7 is neutral, pH < 7 is acidic, and pH > 7 is alkaline.
What is the relationship between hydrogen ion concentration and pH?
pH = -log[H⁺], where [H⁺] is the concentration of hydrogen ions in mol/L.
What is a strong acid?
A strong acid is an acid that completely dissociates in water, releasing all of its hydrogen ions.
What is a weak acid?
A weak acid is an acid that only partially dissociates in water, releasing only a small proportion of its hydrogen ions.
What is a strong base?
A strong base is a base that completely dissociates in water to release hydroxide ions (OH⁻).
What is a weak base?
A weak base is a base that only partially dissociates in water, releasing a small proportion of hydroxide ions.
What is the dissociation constant (Ka) for a weak acid?
Ka is the equilibrium constant for the dissociation of a weak acid in water:
HA ⇌ H⁺ + A⁻
Ka = [H⁺][A⁻] / [HA], where [HA] is the concentration of the undissociated acid.
What is the dissociation constant (Kb) for a weak base?
Kb is the equilibrium constant for the dissociation of a weak base in water:
B + H₂O ⇌ BH⁺ + OH⁻
Kb = [BH⁺][OH⁻] / [B], where [B] is the concentration of the undissociated base.
What is the pKa of an acid?
The pKa is the negative logarithm of the acid dissociation constant (Ka):
pKa = -log(Ka).
The lower the pKa, the stronger the acid.
What is the pKb of a base?
The pKb is the negative logarithm of the base dissociation constant (Kb):
pKb = -log(Kb).
The lower the pKb, the stronger the base.
What is a buffer solution?
A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. It typically contains a weak acid and its conjugate base, or a weak base and its conjugate acid.
What is an acid-base titration?
An acid-base titration is a method used to determine the concentration of an acid or base by neutralizing it with a base or acid of known concentration, using an indicator to identify the endpoint.
What is the equivalence point in an acid-base titration?
The equivalence point is the point at which the amount of acid is stoichiometrically equivalent to the amount of base in the solution, and the reaction is complete.
What is the role of an indicator in an acid-base titration?
An indicator is a substance that changes color at a specific pH range, signaling the endpoint of the titration.
What is a rate equation?
A rate equation shows the relationship between the rate of a chemical reaction and the concentrations of the reactants. It is usually written as:
Rate = k[A]^m[B]^n,
where k is the rate constant, [A] and [B] are the concentrations of reactants, and m and n are their respective orders.
What is the rate constant (k)?
The rate constant (k) is a proportionality constant that links the rate of a reaction to the concentrations of reactants in the rate equation.
It is specific to a reaction at a given temperature and has units that depend on the overall order of the reaction.
What is the order of a reaction with respect to a reactant?
The order of reaction with respect to a reactant (e.g., m in Rate = k[A]^m) refers to the power to which the concentration of the reactant is raised in the rate equation. It indicates how the rate changes as the concentration of that reactant changes.
What is a rate-determining step?
The rate-determining step is the slowest step in a reaction mechanism, which determines the overall rate of the reaction. It is the step with the highest activation energy.
equation for entropy
ΔS = S(final) - S (initial)
when does entropy increase
- solid melts
- liquid boils
- solid dissolves in water
- the number of gas molecules increases
- the temperature increases
