net forward reaction
⚖️ACS GENERAL CHEMISTRY STUDY GUIDE
Equilibrium, Acids, and Bases for the ACS Exam
Practice equilibrium constants, reaction quotients, buffers, titrations, pH, weak-acid calculations, and Le Châtelier reasoning.
8 key ideas8 flashcards5 practice questions
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Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
At equilibrium, forward and reverse rates are equal while macroscopic concentrations stay constant.
- 02
An equilibrium constant uses activities, often approximated by concentrations or partial pressures.
- 03
The reaction quotient Q has the same form as K but uses current amounts.
- 04
Comparing Q with K predicts the net direction toward equilibrium.
- 05
A strong acid or base ionizes nearly fully in dilute water under common course conditions.
- 06
Weak-acid and weak-base calculations connect Ka or Kb with equilibrium concentrations.
- 07
A buffer contains a weak acid-base pair that resists large pH movement after small additions.
- 08
At the half-equivalence point of a weak-acid titration, pH equals pKa under the usual approximation.
PART OF THE ACS GENERAL CHEMISTRY GUIDE
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Open the full ACS General Chemistry guide →Two ideas worth correcting now
NOT QUITE
→Equilibrium means reactant and product concentrations are equal
USE THIS INSTEAD
Forward and reverse rates are equal; concentrations need not match.
NOT QUITE
→A buffer keeps pH perfectly constant
USE THIS INSTEAD
It limits pH movement only within its capacity.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What does Q less than K predict?Show answer ＋
Net reaction toward products.
2Are pure solids included in K expressions?Show answer ＋
No, their activities are constant.
3What is pH?Show answer ＋
Negative base-ten logarithm of hydrogen-ion activity, often approximated with concentration.
4How are Ka and Kb related for a conjugate pair?Show answer ＋
Their product equals Kw at the stated temperature.
5What does a buffer require?Show answer ＋
Appreciable amounts of a weak acid and its conjugate base, or a weak base and its conjugate acid.
6What equation estimates buffer pH?Show answer ＋
Henderson-Hasselbalch: pH = pKa + log(base/acid).
7What is true at a strong acid-strong base equivalence point at 25 °C?Show answer ＋
The solution is neutral if no other acid-base species affect pH.
8Does a catalyst alter K?Show answer ＋
No.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01How does adding reactant affect an equilibrium mixture?
Q falls relative to K, so net forward reaction consumes part of the added reactant.
02Why does dilution favor the side with more dissolved particles in some equilibria?
The concentration terms shift Q, and net reaction proceeds until Q again equals K.
03How is weak-acid pH estimated from Ka and starting concentration?
Set an ICE table, substitute equilibrium amounts into Ka, solve for hydrogen ion, then verify the approximation if used.
04What should happen before using Henderson-Hasselbalch after strong acid is added to a buffer?
Complete the stoichiometric reaction between strong acid and conjugate base, then use remaining buffer amounts.
05Why is equivalence not the same as endpoint?
Equivalence is stoichiometric; endpoint is the observed indicator or instrument signal.
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