What is the standard enthalpy of formation (ΔH°f) of a pure chemical element in its standard reference state?

Exactly zero kJ/mol by definition (e.g., O2(g), C(graphite), N2(g), Fe(s) at 298.15 K and 1 bar).

What is the formula for calculating the percent yield of a chemical reaction?

Percent Yield = (Actual Yield / Theoretical Yield) * 100%.

What is the definition of a mole, and what numerical value represents Avogadro's constant?

The amount of substance containing as many elementary entities as there are atoms in exactly 12 grams of pure carbon-12, equal to 6.022 x 10^23 entities per mole.

Under what temperature conditions is a chemical reaction spontaneous if both ΔH and ΔS are negative (ΔH < 0, ΔS < 0)?

Spontaneous only at low temperatures where the favorable enthalpy term (|ΔH|) outweighs the unfavorable -TΔS term (T < ΔH/ΔS).

How do exothermic and endothermic processes differ in the sign of enthalpy change (ΔH)?

Exothermic processes release heat to the surroundings and have ΔH 0.

Compare the Arrhenius, Brønsted-Lowry, and Lewis definitions of acids and bases.

Arrhenius: acid produces H+, base produces OH- in water; Brønsted-Lowry: acid donates H+, base accepts H+; Lewis: acid accepts an electron pair, base donates an electron pair.

What are the thermodynamic criteria for spontaneity, equilibrium, and non-spontaneity in terms of ΔG at constant T and P?

ΔG 0: Non-spontaneous forward process (spontaneous in reverse).

Define molarity (M) and state the formula used to calculate dilutions.

Molarity is moles of solute per liter of solution (mol/L); dilution formula is M1*V1 = M2*V2.

How is standard reaction enthalpy (ΔH°rxn) calculated from standard enthalpies of formation (ΔH°f)?

ΔH°rxn = Σ [n * ΔH°f(products)] - Σ [m * ΔH°f(reactants)], where n and m are stoichiometric coefficients.

What does the Third Law of Thermodynamics define regarding absolute zero?

The entropy of a perfect, pure crystalline substance at absolute zero (0 Kelvin) is exactly zero (S = 0).

What two chemical components are required to prepare a functional buffer solution?

A weak acid and its conjugate base, or a weak base and its conjugate acid, in comparable molar quantities.

What is the ion-product constant of water (Kw) at 25°C, and what is the relationship between pH and pOH?

Kw = [H+][OH-] = 1.0 x 10^-14 at 25°C; pH + pOH = 14.00.

What is the half-equivalence point in a weak acid titration, and what special pH relationship holds there?

The point where exactly half of the weak acid has been neutralized to conjugate base; at this point, [HA] = [A-] and pH = pKa.

Name the six common strong monoprotic and diprotic acids.

Hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI), nitric acid (HNO3), perchloric acid (HClO4), and sulfuric acid (H2SO4, first proton).

State the First Law of Thermodynamics and write its mathematical equation.

Energy cannot be created or destroyed, only transferred or transformed: ΔU = q + w, where ΔU is internal energy change, q is heat added, and w is work done on the system (w = -PΔV).

Why is the pH at the equivalence point greater than 7 when titrating a weak acid with a strong base?

At equivalence, the weak acid is completely converted into its conjugate base (A-), which hydrolyzes in water: A- + H2O HA + OH-, producing basic OH- ions.

What mathematical relationship connects Ka of a weak acid and Kb of its conjugate base in aqueous solution at 25°C?

Ka * Kb = Kw = 1.0 x 10^-14, or pKa + pKb = 14.00.

What is the difference between a state function and a path function in thermodynamics?

A state function (e.g., U, H, S, G) depends only on the current equilibrium state, not the pathway taken; a path function (e.g., heat q, work w) depends on the specific path taken between states.

Write the Gibbs Free Energy equation relating enthalpy, entropy, and absolute temperature.

ΔG = ΔH - TΔS, where T is the absolute temperature in Kelvin.

What is the mathematical definition of acid dissociation constant (Ka) and pKa?

Ka = [H+][A-] / [HA]; pKa = -log10(Ka). A smaller pKa corresponds to a stronger acid.

Arrange the three classical states of matter (solid, liquid, gas) of a substance in order of increasing entropy.

Solid < Liquid << Gas (gases possess far greater positional disorder and microstates).

Identify the conjugate base of sulfuric acid (H2SO4) and the conjugate acid of ammonia (NH3).

Conjugate base of H2SO4 is bisulfate (HSO4-); conjugate acid of NH3 is ammonium (NH4+).

How does an empirical chemical formula differ from a molecular chemical formula?

The empirical formula gives the simplest whole-number ratio of atoms of each element in a compound; the molecular formula gives the exact actual number of atoms in a molecule.

What does Hess's Law state regarding standard enthalpy changes of chemical reactions?

If a reaction can be expressed as the sum of two or more steps, the total enthalpy change for the overall reaction is the sum of the enthalpy changes for each individual step.

How does molality (m) differ from molarity (M), and why is molality preferred in colligative property calculations?

Molality is moles of solute per kilogram of solvent (mol/kg); unlike molarity, molality is independent of temperature because mass does not expand or contract with temperature changes.

Under what temperature conditions is a chemical reaction spontaneous if both ΔH and ΔS are positive (ΔH > 0, ΔS > 0)?

Spontaneous only at high temperatures where the favorable -TΔS term outweighs the endothermic enthalpy term (T > ΔH/ΔS).

When does a buffer system exhibit its maximum buffer capacity?

When the molar concentrations of the weak acid and its conjugate base are equal ([A-] = [HA]), at which point pH = pKa.

What is the Henderson-Hasselbalch equation for calculating the pH of a buffer solution?

pH = pKa + log10([A-] / [HA]), where [A-] is conjugate base and [HA] is weak acid concentration.

What is a limiting reactant in a chemical reaction, and how is it identified mathematically?

The reactant that is completely consumed first, limiting the amount of product formed; identified by dividing the moles of each reactant by its stoichiometric coefficient.

State the Second Law of Thermodynamics in terms of universe entropy.

In any spontaneous thermodynamic process, the total entropy of the universe (system + surroundings) always increases: ΔSuniverse = ΔSsystem + ΔSsurroundings > 0.

What is the difference between the equivalence point and the endpoint of an acid-base titration?

The equivalence point is the stoichiometric point where moles of base equal moles of acid added; the endpoint is the point where the chemical indicator changes color.

Analytical Chemistry (Intermediate): Stoichiometry, Acids/Bases & Thermodynamics

Mole concept, limiting reactants, solution concentration, pH, buffer systems, enthalpy, entropy, and Gibbs free energy

Level: intermediate
Languages: en → en
Cards: 32
Markdown: Analytical Chemistry (Intermediate): Stoichiometry, Acids/Bases & Thermodynamics (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	What is the standard enthalpy of formation (ΔH°f) of a pure chemical element in its standard reference state?	Exactly zero kJ/mol by definition (e.g., O2(g), C(graphite), N2(g), Fe(s) at 298.15 K and 1 bar).
2	What is the formula for calculating the percent yield of a chemical reaction?	Percent Yield = (Actual Yield / Theoretical Yield) * 100%.
3	What is the definition of a mole, and what numerical value represents Avogadro's constant?	The amount of substance containing as many elementary entities as there are atoms in exactly 12 grams of pure carbon-12, equal to 6.022 x 10^23 entities per mole.
4	Under what temperature conditions is a chemical reaction spontaneous if both ΔH and ΔS are negative (ΔH < 0, ΔS < 0)?	Spontaneous only at low temperatures where the favorable enthalpy term (\|ΔH\|) outweighs the unfavorable -TΔS term (T < ΔH/ΔS).
5	How do exothermic and endothermic processes differ in the sign of enthalpy change (ΔH)?	Exothermic processes release heat to the surroundings and have ΔH < 0; endothermic processes absorb heat from the surroundings and have ΔH > 0.
6	Compare the Arrhenius, Brønsted-Lowry, and Lewis definitions of acids and bases.	Arrhenius: acid produces H+, base produces OH- in water; Brønsted-Lowry: acid donates H+, base accepts H+; Lewis: acid accepts an electron pair, base donates an electron pair.
7	What are the thermodynamic criteria for spontaneity, equilibrium, and non-spontaneity in terms of ΔG at constant T and P?	ΔG < 0: Spontaneous forward process; ΔG = 0: Dynamic equilibrium; ΔG > 0: Non-spontaneous forward process (spontaneous in reverse).
8	Define molarity (M) and state the formula used to calculate dilutions.	Molarity is moles of solute per liter of solution (mol/L); dilution formula is M1V1 = M2V2.
9	How is standard reaction enthalpy (ΔH°rxn) calculated from standard enthalpies of formation (ΔH°f)?	ΔH°rxn = Σ [n * ΔH°f(products)] - Σ [m * ΔH°f(reactants)], where n and m are stoichiometric coefficients.
10	What does the Third Law of Thermodynamics define regarding absolute zero?	The entropy of a perfect, pure crystalline substance at absolute zero (0 Kelvin) is exactly zero (S = 0).
11	What two chemical components are required to prepare a functional buffer solution?	A weak acid and its conjugate base, or a weak base and its conjugate acid, in comparable molar quantities.
12	What is the ion-product constant of water (Kw) at 25°C, and what is the relationship between pH and pOH?	Kw = [H+][OH-] = 1.0 x 10^-14 at 25°C; pH + pOH = 14.00.
13	What is the half-equivalence point in a weak acid titration, and what special pH relationship holds there?	The point where exactly half of the weak acid has been neutralized to conjugate base; at this point, [HA] = [A-] and pH = pKa.
14	Name the six common strong monoprotic and diprotic acids.	Hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI), nitric acid (HNO3), perchloric acid (HClO4), and sulfuric acid (H2SO4, first proton).
15	State the First Law of Thermodynamics and write its mathematical equation.	Energy cannot be created or destroyed, only transferred or transformed: ΔU = q + w, where ΔU is internal energy change, q is heat added, and w is work done on the system (w = -PΔV).
16	Why is the pH at the equivalence point greater than 7 when titrating a weak acid with a strong base?	At equivalence, the weak acid is completely converted into its conjugate base (A-), which hydrolyzes in water: A- + H2O <-> HA + OH-, producing basic OH- ions.
17	What mathematical relationship connects Ka of a weak acid and Kb of its conjugate base in aqueous solution at 25°C?	Ka * Kb = Kw = 1.0 x 10^-14, or pKa + pKb = 14.00.
18	What is the difference between a state function and a path function in thermodynamics?	A state function (e.g., U, H, S, G) depends only on the current equilibrium state, not the pathway taken; a path function (e.g., heat q, work w) depends on the specific path taken between states.
19	Write the Gibbs Free Energy equation relating enthalpy, entropy, and absolute temperature.	ΔG = ΔH - TΔS, where T is the absolute temperature in Kelvin.
20	What is the mathematical definition of acid dissociation constant (Ka) and pKa?	Ka = [H+][A-] / [HA]; pKa = -log10(Ka). A smaller pKa corresponds to a stronger acid.
21	Arrange the three classical states of matter (solid, liquid, gas) of a substance in order of increasing entropy.	Solid < Liquid << Gas (gases possess far greater positional disorder and microstates).
22	Identify the conjugate base of sulfuric acid (H2SO4) and the conjugate acid of ammonia (NH3).	Conjugate base of H2SO4 is bisulfate (HSO4-); conjugate acid of NH3 is ammonium (NH4+).
23	How does an empirical chemical formula differ from a molecular chemical formula?	The empirical formula gives the simplest whole-number ratio of atoms of each element in a compound; the molecular formula gives the exact actual number of atoms in a molecule.
24	What equation relates heat transfer (q) to mass (m), specific heat capacity (c), and temperature change (ΔT)?	q = m * c * ΔT.
25	What does Hess's Law state regarding standard enthalpy changes of chemical reactions?	If a reaction can be expressed as the sum of two or more steps, the total enthalpy change for the overall reaction is the sum of the enthalpy changes for each individual step.
26	How does molality (m) differ from molarity (M), and why is molality preferred in colligative property calculations?	Molality is moles of solute per kilogram of solvent (mol/kg); unlike molarity, molality is independent of temperature because mass does not expand or contract with temperature changes.
27	Under what temperature conditions is a chemical reaction spontaneous if both ΔH and ΔS are positive (ΔH > 0, ΔS > 0)?	Spontaneous only at high temperatures where the favorable -TΔS term outweighs the endothermic enthalpy term (T > ΔH/ΔS).
28	When does a buffer system exhibit its maximum buffer capacity?	When the molar concentrations of the weak acid and its conjugate base are equal ([A-] = [HA]), at which point pH = pKa.
29	What is the Henderson-Hasselbalch equation for calculating the pH of a buffer solution?	pH = pKa + log10([A-] / [HA]), where [A-] is conjugate base and [HA] is weak acid concentration.
30	What is a limiting reactant in a chemical reaction, and how is it identified mathematically?	The reactant that is completely consumed first, limiting the amount of product formed; identified by dividing the moles of each reactant by its stoichiometric coefficient.
31	State the Second Law of Thermodynamics in terms of universe entropy.	In any spontaneous thermodynamic process, the total entropy of the universe (system + surroundings) always increases: ΔSuniverse = ΔSsystem + ΔSsurroundings > 0.
32	What is the difference between the equivalence point and the endpoint of an acid-base titration?	The equivalence point is the stoichiometric point where moles of base equal moles of acid added; the endpoint is the point where the chemical indicator changes color.