2026 Updated HESI A2 Chemistry Study Guide
*1. CHEMISTRY - Chemical Kinetics*
● A nursing student is studying the decomposition of hydrogen peroxide (2H2O2 -> 2H2O
+ O2) catalyzed by iodide ions. The student measures the rate and finds Rate =
k[H2O2][I-]. The student doubles the concentration of H2O2 while keeping [I-] constant
and observes the rate. The student then doubles [I-] as well. Explain what happens to
the rate in each case and determine the overall reaction order. What would be the effect
of adding a catalyst on the activation energy?
A) Rate doubles then quadruples, overall order 2, catalyst lowers Ea
B) Rate stays same, order 1, catalyst increases Ea
C) Rate quadruples then octuples, order 3, catalyst has no effect
D) Rate halves, order 0, catalyst increases Ea
*Answer: A* - First order in each, overall second order. Catalyst lowers activation energy,
increasing rate.
*2.* A solution contains 0.5M HCl. A student adds 0.5M NaOH in equal volume. The student
measures pH before and after mixing. The student also tests the effect of temperature on the
neutralization rate from 25°C to 50°C. What is the pH after mixing and what happens to the rate
when temperature increases?
A) pH 7 neutral, rate increases with temperature
B) pH 1 acidic, rate decreases
C) pH 14 basic, rate stays same
D) pH 0 acidic, rate halves
*Answer: A*
*3.* The Arrhenius equation is k = Ae^(-Ea/RT). A student plots ln(k) vs 1/T and gets a straight
line. The slope is -Ea/R. The student has two reactions: Reaction X with Ea = 50 kJ/mol and
Reaction Y with Ea = 100 kJ/mol. At the same temperature, which has higher k and why?
A) X higher k because lower Ea, easier to overcome barrier
B) Y higher k because higher Ea
C) Both same k
D) Cannot determine
*Answer: A*
*4.* For reaction N2O4 ⇌ 2NO2, Keq = 0.36 at 100°C. A student adds more N2O4 to an
equilibrium mixture and observes color change (N2O4 colorless, NO2 brown). According to Le
Chatelier's principle, which direction will the reaction shift and what happens to the brown color?
A) Shifts to products, brown color intensifies
B) Shifts to reactants, brown fades
*1. CHEMISTRY - Chemical Kinetics*
● A nursing student is studying the decomposition of hydrogen peroxide (2H2O2 -> 2H2O
+ O2) catalyzed by iodide ions. The student measures the rate and finds Rate =
k[H2O2][I-]. The student doubles the concentration of H2O2 while keeping [I-] constant
and observes the rate. The student then doubles [I-] as well. Explain what happens to
the rate in each case and determine the overall reaction order. What would be the effect
of adding a catalyst on the activation energy?
A) Rate doubles then quadruples, overall order 2, catalyst lowers Ea
B) Rate stays same, order 1, catalyst increases Ea
C) Rate quadruples then octuples, order 3, catalyst has no effect
D) Rate halves, order 0, catalyst increases Ea
*Answer: A* - First order in each, overall second order. Catalyst lowers activation energy,
increasing rate.
*2.* A solution contains 0.5M HCl. A student adds 0.5M NaOH in equal volume. The student
measures pH before and after mixing. The student also tests the effect of temperature on the
neutralization rate from 25°C to 50°C. What is the pH after mixing and what happens to the rate
when temperature increases?
A) pH 7 neutral, rate increases with temperature
B) pH 1 acidic, rate decreases
C) pH 14 basic, rate stays same
D) pH 0 acidic, rate halves
*Answer: A*
*3.* The Arrhenius equation is k = Ae^(-Ea/RT). A student plots ln(k) vs 1/T and gets a straight
line. The slope is -Ea/R. The student has two reactions: Reaction X with Ea = 50 kJ/mol and
Reaction Y with Ea = 100 kJ/mol. At the same temperature, which has higher k and why?
A) X higher k because lower Ea, easier to overcome barrier
B) Y higher k because higher Ea
C) Both same k
D) Cannot determine
*Answer: A*
*4.* For reaction N2O4 ⇌ 2NO2, Keq = 0.36 at 100°C. A student adds more N2O4 to an
equilibrium mixture and observes color change (N2O4 colorless, NO2 brown). According to Le
Chatelier's principle, which direction will the reaction shift and what happens to the brown color?
A) Shifts to products, brown color intensifies
B) Shifts to reactants, brown fades
