Acid-Base Equilibria
What is the pH of a neutral solution at 25°C?
7
What is the first law of thermodynamics?
Energy cannot be created or destroyed, only transformed.
What is the rate law expression for a reaction with the following rate constant units: L/(mol·s)?
The reaction is second-order with respect to the reactant.
What is the definition of oxidation in a redox reaction?
Oxidation is the loss of electrons.
What type of bonding is present in an ionic compound like NaCl?
Ionic bonding.
Which of the following is a strong acid: HCl, HNO₃, CH₃COOH, NH₃?
HCl and HNO₃ (both are strong acids)
Define enthalpy (ΔH) in terms of heat flow at constant pressure.
Enthalpy is the heat content of a system, and ΔH = heat absorbed or released at constant pressure.
In the reaction A → B, the concentration of A decreases by half in 10 minutes. What is the order of the reaction?
First-order (since the half-life is constant for first-order reactions).
In a galvanic cell, which electrode is the site of reduction?
The cathode.
What is the molecular geometry of CO₂?
Linear.
Calculate the pH of a 0.1 M NaOH solution.
pH = 13 (pOH = 1, pH = 14 - pOH)
What is the standard enthalpy change of formation for any element in its most stable form?
0 kJ/mol
What is the effect on the rate of a reaction when the temperature is increased by 10°C?
The rate typically doubles for every 10°C increase (based on the Arrhenius equation).
What is the standard electrode potential of the half-reaction Zn²⁺ + 2e⁻ → Zn?
-0.76 V
How many sigma and pi bonds are in a triple bond between two carbon atoms?
1 sigma bond and 2 pi bonds.
A 0.10 M solution of formic acid (HCOOH) has a pH of 2.38. Calculate the Ka of formic acid.
Ka = 1.6 × 10⁻⁴ (Use the formula pH=−log[H+]pH=−log[H+], find [H⁺], and then apply the expression for Ka)
A reaction has ΔG = -25 kJ/mol. What does this indicate about the spontaneity of the reaction?
The reaction is spontaneous (since ΔG is negative).
Given the following data for the reaction 2A → B:
[A] (M) at time 0: 0.5, [A] at time 30s: 0.3.
What is the rate constant if the reaction is first-order?
k = 0.0231 s⁻¹ (using the integrated first-order rate law: ln([A₀]/[A]) = kt)
Calculate the cell potential for a galvanic cell consisting of a Cu/Cu²⁺ half-cell and a Zn/Zn²⁺ half-cell (E°(Cu²⁺/Cu) = +0.34 V, E°(Zn²⁺/Zn) = -0.76 V).
Ecell = +1.10 V (Ecell = E°(cathode) - E°(anode) = 0.34 - (-0.76))
What is the hybridization of the central atom in CH₄?
sp³
A buffer solution is prepared with 0.15 M NH₃ and 0.10 M NH₄Cl. What is the pH of the solution if the pKa of ammonium ion (NH₄⁺) is 9.25?
pH = 9.13 (Using the Henderson-Hasselbalch equation: pH=pKa+log([NH₃][NH₄⁺])pH=pKa+log([NH₄⁺][NH₃]))
Calculate the entropy change (ΔS) for a process in which ΔG = ΔH - TΔS at 298 K, given that ΔG = -150 kJ/mol and ΔH = -200 kJ/mol.
ΔS = +167 J/mol·K (ΔS = (ΔH - ΔG) / T = (-200,000 J/mol + 150,000 J/mol) / 298 K)
For the reaction 2N₂O₅ → 4NO₂ + O₂, the activation energy is 75 kJ/mol. If the rate doubles when the temperature is increased by 10°C, what is the temperature increase?
10°C increase (the rate doubling corresponds to a 10°C increase in temperature based on the rule of thumb).
A galvanic cell consists of a silver electrode in a 1 M AgNO₃ solution and a copper electrode in a 1 M CuSO₄ solution. The cell potential is 0.46 V. Calculate the concentration of Cu²⁺. (E°(Ag+/Ag) = +0.80 V, E°(Cu²⁺/Cu) = +0.34 V)
[Cu²⁺] = 0.056 M (using the Nernst equation)
Predict the bond angle in a molecule with trigonal planar geometry, such as BF₃.
120°