Set up an Ice Table (Initial, Change, Equilibrium) based on this stoichiometry:
[ \Delta H^\circ_rxn = \sum \Delta H_f^\circ (\textproducts) - \sum \Delta H_f^\circ (\textreactants) ] [ = [2(-94.1) + 1(-68.3)] - [1(+54.2) + \frac52(0)] ] [ = [-188.2 - 68.3] - [54.2] ] [ = -256.5 - 54.2 = -310.7 , \textkcal/mol ]
$$ \textMoles O = \frac0.211\text g16.0\text g/mol = 0.0132\text mol $$
, specific worked answers for that year are often found in categorized worksheets rather than a single modern scoring guideline. chemmybear.com Below is the solution for the 1972 Free Response Question on Gas Laws
To find the standard electromotive force of the cell, identify the reduction and oxidation half-reactions. Use the standard reduction potential table:
This article provides a comprehensive overview of the types of questions featured in 1972, the foundational concepts they covered, and how to utilize them for your AP Chemistry studies in 2026. The Landscape of the 1972 AP Chemistry Exam
1972 AP Chemistry Free Response Answers: A Historical Overview and Review
Calculating the electromotive force (EMF) of a galvanic cell was a staple of the free-response section.
PCl5(g)⇌PCl3(g)+Cl2(g)cap P cap C l sub 5 open paren g close paren is in equilibrium with cap P cap C l sub 3 open paren g close paren plus cap C l sub 2 open paren g close paren
Let ( s ) = molar solubility. ( K_sp = [Pb^2+][F^-]^2 = (s)(2s)^2 = 4s^3 ) ( 4s^3 = 3.7 \times 10^-8 ) ( s^3 = 9.25 \times 10^-9 ) ( s = \sqrt[3]9.25 \times 10^-9 ) ( s \approx 2.10 \times 10^-3 , \textM )
Given a solution of ammonium chloride. What additional reagent or reagents are needed to prepare a buffer from the ammonium chloride solution? Explain how this buffer solution resists a change in pH when:
A weak acid or weak base titration scenario. This problem tests a student's ability to calculate the pH at various points of a titration curve: the initial weak acid solution, the buffer region, the equivalence point, and post-equivalence. Mathematical Walkthrough
Students were typically asked to calculate the degree of dissociation and the equilibrium constant Kpcap K sub p for the reaction: