CHEMISTRY · RAPID REFERENCE

MDCAT Chemistry Formula & Equation Sheet — Concepts, Conditions & Traps

A dense but structured chemistry reference covering the relationships students repeatedly need to retrieve: moles, solutions, gases, equilibrium, acids and bases, thermochemistry, electrochemistry and core organic logic.

Study Tools / Informational / MDCAT Chemistry Formula & Equation Sheet — Concepts, Conditions & Traps
Research edition · Updated 19 September 2026 · Built for MDCAT study and reference
Research note: This page combines PM&DC curriculum context with standard scientific references. It is designed as a study aid; the current official syllabus and examination notices remain the source of truth for exam-specific requirements.
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Chemistry questions in the 2026 pattern
10³
Prefixes can shift results by orders of magnitude
pH
Logarithms matter
Official-context note: Use this as a revision sheet after learning the underlying concepts. Chemistry equations often carry hidden conditions — concentration vs amount, equilibrium vs initial composition, standard-state conventions, idealized vs real behavior — so the “when to use it” column matters as much as the equation itself.

Quick Reference

Quick take

Balance first

Stoichiometric arithmetic is unreliable if the chemical equation is not balanced.

Quick take

Track units

Moles, molarity, volume, mass and particles are related but not interchangeable.

Quick take

Logs reverse intuition

A smaller pH corresponds to a higher hydrogen-ion concentration.

Quick take

Equilibrium is dynamic

Forward and reverse reactions continue; equilibrium describes equal rates, not equal concentrations.

1. Mole, Molarity & Stoichiometry

Core relationships
n = m/M · N = nN_A · M = n/V
n = amount in moles, m = mass, M = molar mass, N = number of particles, V = solution volume in liters for molarity.

For reaction calculations, the balanced equation supplies the mole ratios. The limiting reactant is the reactant that is consumed first according to those ratios; the theoretical yield is set by that limiting reagent, not by whichever reactant has the larger numerical amount.

2. Gases & Solutions

RelationshipUseWatch
PV = nRTIdeal-gas state relationship.Temperature must be absolute (K).
d = m/VDensity.Keep volume units consistent with mass units.
M₁V₁ = M₂V₂Dilution of the same solute.It assumes the amount of solute is conserved during dilution.
moles = M × VConvert molarity and liters to moles.Do not use mL without conversion.

3. Thermochemistry

Common relationships
q = mcΔT · ΔH = H_products − H_reactants · ΔG = ΔH − TΔS
The exact level of thermodynamic treatment should match the syllabus and course text; keep the sign convention explicit.

A positive heat flow into a system and a negative heat flow out of a system are descriptions that depend on the convention used. Do not memorize signs in isolation; write what the system is doing and then apply the chosen convention consistently.

4. Chemical Equilibrium

General equilibrium form
K_c = (product concentrations) / (reactant concentrations), each raised to its stoichiometric coefficient

Only species included in the equilibrium expression belong in the numerical form used for concentration-based equilibrium problems; pure solids and liquids are treated differently in the standard equilibrium expression. Le Châtelier’s principle is a qualitative response model: when a system at equilibrium is disturbed, the composition shifts in a direction that opposes the imposed change.

5. Acids, Bases, pH, pKa, Ka, Kb & Kw

Core relationships
pH = −log₁₀[H⁺] · pOH = −log₁₀[OH⁻] · pK_a = −log₁₀K_a · pK_b = −log₁₀K_b
At 25 °C in dilute aqueous conditions, the familiar relation pH + pOH = 14 is used. Temperature dependence matters outside that context.

IUPAC defines Ka as an equilibrium constant for acid dissociation and notes the use of pKa as its negative base-10 logarithm. At the same general conditions, a larger Ka corresponds to greater acid dissociation; therefore a smaller pKa indicates a stronger acid.

6. Electrochemistry

Useful equations
E°_cell = E°_cathode − E°_anode · ΔG° = −nFE°_cell

Keep oxidation at the anode and reduction at the cathode straight. In galvanic-cell problems, a spontaneous cell reaction corresponds to a positive standard cell potential under the stated conventions. For calculations, make a small sign table rather than relying on memory alone.

7. Organic Chemistry: A Pattern Library

Organic chemistry often feels like a list until you stop memorizing individual reactions and start organizing compounds by functional group and reaction type. Build a map:

Hydrocarbon

Alkane / alkene / alkyne

Track saturation and the characteristic reactions associated with the carbon framework.

Oxygen

Alcohols / phenols / acids

Watch functional-group identity, oxidation state and acidity differences.

Halogens

Alkyl halides

Focus on the carbon–halogen bond and the type of transformation being tested.

Biochemistry

Biomolecules

Connect structure to function rather than learning isolated names.

Frequently Asked Questions

Why do chemistry calculations go wrong even when I know the formula?
The usual failure is upstream: unbalanced equations, wrong units, incorrect stoichiometric ratios, wrong temperature scale or a misunderstanding of what the symbols represent.
When can I use pH + pOH = 14?
The familiar 14 relation is the 25 °C aqueous shortcut. The actual ion-product of water varies with temperature, so do not treat 14 as a universal constant.
Is a larger Ka always a stronger acid?
At the same general conditions, larger Ka means greater dissociation tendency and therefore greater acid strength in the usual equilibrium sense.
Should I memorize organic reactions individually?
Use functional-group and reaction-pattern organization first. It reduces the number of disconnected facts you must retrieve.
Research & reference sources:
PM&DC — Uniform Curriculum MDCAT-2025 (official PDF) · PM&DC — Public Notice regarding MDCAT-2026 · IUPAC Gold Book — acid dissociation constant · OpenStax — College Physics 2e: Physical Quantities, Units, Accuracy & Significant Figures

Scope: scientific explanations are written for student use and simplified where appropriate. Exact exam wording, syllabus scope and current administrative rules should be checked against PM&DC documents.