A ruled notebook open on a desk under a lamp at night, with a mechanical pencil resting in the binding and a mug beside it

Published September 22, 2026 · Flasky Editorial Team · fact-checked against the sources below

A chemistry formula sheet is only useful when each entry carries the condition that makes it legal to use. This one groups the relationships a first-year course actually reaches for, says what each one requires, and links every entry to a page that works it through with real numbers and units.

Most sheets are a wall of symbols, and that is the weakness of the format. The symbols are the part anyone can look up in ten seconds. The conditions decide whether the answer comes out right, and they are almost never printed next to the equation. PV = nRT needs kelvin and a value of R that matches your pressure unit, and neither is written in the four letters.

So every entry below is a link. The name and the relationship are here; the conditions, the variable list, the common mistakes and a worked example live on the page behind it.

What belongs on a chemistry formula sheet?

Three things, in this order. The relationship itself. The meaning and unit of every symbol in it, because a formula with an unlabeled symbol is not a formula. And the conditions under which it holds, which is the entry most sheets omit and the entry that does the work.

Stoichiometry: which relationship does the problem need?

Every one of these turns a measurable quantity into moles, moves through the balanced equation, and turns moles back into something measurable. That is the whole subject: atoms are conserved, and the coefficients are the exchange rate.

Mass and moles. Molar mass is the sum over each element of (atoms multiplied by atomic mass), with n = m / M going from grams to moles and m = n x M going back. For calcium carbonate, using the IUPAC abridged atomic weights Ca 40.078, C 12.011 and O 15.999, the molar mass is 40.078 + 12.011 + 3(15.999) = 100.086, which rounds to 100.09 g/mol. Nothing else here works until this conversion is done.

Composition. The empirical formula comes from percent composition: take a 100 g sample, convert each element’s mass to moles, divide by the smallest result, then clear any fraction. The molecular formula is that multiplied by n = molar mass / empirical formula mass.

Which reactant runs out. The limiting reactant is found by comparing n(X) divided by the coefficient of X across the reactants, with the smallest value limiting. OpenStax gives the same test the other way around: compute the product expected from each reactant on its own and keep the smaller.

How much you actually got. Percent yield is (actual yield / theoretical yield) x 100%, where the theoretical yield is what the limiting reactant allows. A reaction with a theoretical yield of 12.5 g that produces 10.7 g has a percent yield of (10.7 / 12.5) x 100% = 85.6%, to three significant figures.

Atomic structure and bonding: which of these is not a formula?

Two of the three. Electron configuration is a notation with rules rather than a relationship between variables: fill in the Aufbau order 1s 2s 2p 3s 3p 4s 3d 4p and onward, at most two electrons per orbital, and spread electrons singly across equal-energy orbitals before pairing them. Lewis structures are a procedure too, though the arithmetic matters: formal charge, FC = (valence electrons) minus (lone pair electrons) minus half the bonding electrons, settles an argument between two structures that both satisfy the octet rule.

Covalent bonding does carry a number: the electronegativity difference between two atoms sorts the bond from essentially pure covalent through polar covalent to ionic. The cut-offs between those bands are a teaching convention rather than a law of nature, and courses do not all use the same ones, so take yours from your own text and keep the page for the reasoning.

Solutions and acids: where do the units go wrong?

In the definition of molarity, usually, and then in everything downstream of it. Molarity is moles of solute divided by liters of solution, and OpenStax is explicit that this means the volume of the finished solution rather than the solvent you started with, which is why a volumetric flask is filled to a mark. The dilution relation C1V1 = C2V2 follows from that, and works only because adding solvent does not change the amount of solute. To make 250.0 mL of 0.100 M solution from a 2.00 M stock, V1 = C2V2 / C1 = (0.100 M x 0.2500 L) / 2.00 M = 0.0125 L, which is 12.5 mL of stock diluted to the mark.

pH is -log[H3O+], with [H3O+] = 10^(-pH) going back the other way. At 25 degrees Celsius, Kw = [H3O+][OH-] = 1.0 x 10^-14, which is where pH + pOH = 14.00 comes from, and that 14.00 is a fact about room temperature rather than about water. A solution with [H3O+] = 2.5 x 10^-3 M has pH = -log(2.5 x 10^-3) = 2.60, so at 25 degrees Celsius its pOH is 14.00 - 2.60 = 11.40. From there the Henderson-Hasselbalch equation pH = pKa + log([A-] / [HA]) handles buffers, collapsing to pH = pKa when the two concentrations are equal, and titration arithmetic runs n(titrant) = M x V at the buret, the mole ratio, then M(analyte) = n(analyte) / V(analyte). The shortcut MaVa = MbVb is valid only for a monoprotic acid against a monoprotic base.

Gases: why does this one relationship break so many answers?

Because it holds three unit traps and shows none of them. The ideal gas law is PV = nRT, and OpenStax states flatly that temperatures must be on the kelvin scale for any gas law calculation. Celsius there is not a small error, it is a different answer. The second trap is R itself: OpenStax gives 0.08206 L atm per mol per K and 8.314 kPa L per mol per K, and the one you pick dictates the pressure unit for the whole problem. The third is that this is ideal behavior, which OpenStax says is only a reasonable assumption at relatively low pressure and high temperature.

For a fixed amount of gas between two states, P1V1 / T1 = P2V2 / T2, and the molar volume every course quotes follows directly. At standard temperature and pressure, which OpenStax defines as 273.15 K and 1 atm, V = nRT / P = (1 mol x 0.08206 L atm per mol per K x 273.15 K) / 1 atm = 22.41 L per mole.

Thermodynamics and kinetics: what do these add?

Direction and speed, which stoichiometry says nothing about. Hess’s law says enthalpy changes add: reverse a step and its sign flips, scale a step and it scales too. The Gibbs free energy equation is G = H - TS, applied as the change at constant temperature, and it decides direction. Rate laws take the form rate = k[A]^m[B]^n, where the orders come from experiment and never from the coefficients, which is the most common misreading in kinetics. The Arrhenius equation k = A e^(-Ea / RT) plots as ln k against 1/T when you want an activation energy. The half-life relationship t½ = ln 2 / k holds only for first-order kinetics; zero and second order have their own expressions on the same page. The Nernst equation closes the set, linking cell potential to concentration away from standard conditions.

Which constants belong on the sheet?

The ones you will use, at the precision you will use them, taken from a published table rather than from memory. The Avogadro constant is exactly 6.02214076 x 10^23 per mole in the NIST CODATA 2022 values, exact because the mole is now defined by it, and 6.022 x 10^23 is the working form. The gas constant is 0.08206 L atm per mol per K or 8.314 kPa L per mol per K, as above. Atomic weights belong in the same category: the IUPAC abridged table gives hydrogen as 1.0080, carbon as 12.011, oxygen as 15.999, sodium as 22.990, chlorine as 35.45 and calcium as 40.078. Half-remembered values are how a molar mass comes out a unit light and a whole chain of conversions inherits the error.

How do you use a sheet while you are working?

Late. The sheet is for the fourth step, not the first. The method on how to solve chemistry problems puts the formula after the balanced equation, the list of givens with units, and the conversion to moles, because scanning a sheet for symbols that match your variables is how a molarity ends up per liter of solvent and a gas calculation ends up in Celsius. Read the conditions before the equation. If one does not hold, that is the wrong relationship, and you have saved yourself a page of arithmetic.

This is where a sheet stops being able to help and a tutor can. Flasky’s formula sheet carries the conditions next to each relationship, and if you photograph the problem you are stuck on, it names the conversion, says why that one, and shows the working line by line so you can see which step would have gone wrong. Every step is visible on purpose, because the aim is to do the next one without asking.

The full set, with the variables, the conditions and a worked example on every page, lives at chemistry formulas.

Sources