Chemistry Formulas – Complete List & Examples
Chemistry formulas are symbolic ways to write substances, reactions, quantities, and relationships used in chemistry problems. Use this page to find a formula by class, chapter, or topic, then check the worked examples to see how it is applied with units and steps.
Author: Greya Lakshmi, Academic Editor
Chemistry is a branch of science that studies the preparation, properties, structure, composition, and reactions of material substances. It is often called the science of atoms and molecules because it explains how atoms combine, how molecules form, and how substances change during chemical reactions. The study of chemistry also helps students understand daily-life processes such as cooking, cleaning, medicines, fuels, corrosion, water treatment, and environmental protection.
Chemistry Formulas: Complete List
The table below gives the chemistry formulas used most often from Classes 9 to 12. Read the meaning with the formula; do not memorise a symbol without knowing what it represents.
| Topic | Formula | Use |
|---|---|---|
| Temperature | \( K = {}^\circ C + 273 \) | Convert Celsius to Kelvin for gas-law and thermodynamics questions. |
| Density | \( \rho = \frac{m}{V} \) | Find density from mass and volume. |
| Moles from mass | \( n = \frac{m}{M} \) | Convert given mass into moles. |
| Particles from moles | \( N = nN_A \) | Use \( N_A = 6.022 \times 10^{23}\ \text{mol}^{-1} \). |
| Mass percentage | \( \text{Mass percentage} = \frac{\text{mass of component}}{\text{total mass}} \times 100 \) | Used in mixtures, solutions, and composition questions. |
| Percentage composition | \( \%\text{ of element} = \frac{\text{mass of element in compound}}{\text{molar mass of compound}} \times 100 \) | Used before empirical formula calculation. |
| Molecular formula | \( \text{Molecular formula} = n \times \text{empirical formula} \) | Here \( n=\frac{\text{molar mass}}{\text{empirical formula mass}} \). |
| Number of neutrons | \( \text{neutrons} = A – Z \) | \( A \) is mass number and \( Z \) is atomic number. |
| Shell capacity | \( 2n^2 \) | Maximum electrons in shell number \( n \). |
| pH | \( \text{pH} = -\log[H^+] \) | Compare acidity of aqueous solutions. |
| pH and pOH | \( \text{pH}+\text{pOH}=14 \) | Valid for aqueous solutions at \( 25^\circ\text{C} \). |
| Molarity | \( M = \frac{n}{V} \) | Volume must be in litres. |
| Molality | \( m = \frac{n_{\text{solute}}}{\text{mass of solvent in kg}} \) | Used in colligative properties. |
| Mole fraction | \( x_A = \frac{n_A}{n_A+n_B} \) | Fraction of moles of component \( A \). |
| Dilution | \( M_1V_1=M_2V_2 \) | Used when a stock solution is diluted. |
| Ideal gas equation | \( PV=nRT \) | Relates pressure, volume, moles, and temperature. |
| Boyle’s law | \( P_1V_1=P_2V_2 \) | For constant temperature and fixed amount of gas. |
| Charles’ law | \( \frac{V_1}{T_1}=\frac{V_2}{T_2} \) | Temperature must be in Kelvin. |
| First law of thermodynamics | \( \Delta U=q+w \) | Relates internal energy, heat, and work. |
| Enthalpy | \( H=U+PV \) | Used in heat changes at constant pressure. |
| Gibbs energy | \( \Delta G=\Delta H-T\Delta S \) | Used to discuss spontaneity under stated conditions. |
| Equilibrium constant | \( K_c=\frac{[C]^c[D]^d}{[A]^a[B]^b} \) | For \( aA+bB \rightleftharpoons cC+dD \). |
| Ionic product of water | \( K_w=[H^+][OH^-] \) | At \( 25^\circ\text{C} \), \( K_w=1.0\times10^{-14} \). |
| Oxidation number | \( \sum \text{oxidation numbers}=\text{charge on species} \) | Used to find unknown oxidation number. |
| Nernst equation | \( E_{\text{cell}}=E^\circ_{\text{cell}}-\frac{0.0591}{n}\log Q \) | Used at \( 298\ \text{K} \) for electrochemical cells. |
| Charge | \( Q=It \) | Charge equals current multiplied by time. |
| Electrolysis mass | \( m=\frac{EIt}{F} \) | \( F \approx 96500\ \text{C mol}^{-1} \). |
| Rate of reaction | \( \text{Rate}=-\frac{\Delta[A]}{\Delta t}=\frac{\Delta[P]}{\Delta t} \) | Reactant decreases and product increases. |
| First-order rate law | \( k=\frac{2.303}{t}\log\frac{[A]_0}{[A]} \) | Used for first-order reactions. |
| First-order half-life | \( t_{1/2}=\frac{0.693}{k} \) | Independent of initial concentration. |
| Elevation in boiling point | \( \Delta T_b=K_bm \) | Used for dilute solutions. |
| Depression in freezing point | \( \Delta T_f=K_fm \) | Used to find molar mass of solute. |
| Osmotic pressure | \( \pi=CRT \) | Used for dilute solutions. |
| Alkane | \( C_nH_{2n+2} \) | Open-chain saturated hydrocarbons. |
| Alkene | \( C_nH_{2n} \) | Open-chain hydrocarbons with one double bond. |
| Alkyne | \( C_nH_{2n-2} \) | Open-chain hydrocarbons with one triple bond. |
Chemistry Formulas by Class and Chapter
Use this section to connect the formula with the chapter. Chapter names can vary slightly by edition, but the formula ideas below are stable for school chemistry.
Class 9 Formula Map
| Chapter or unit | Formula focus | Key formulas |
|---|---|---|
| Matter in Our Surroundings | Temperature and density | \( K={}^\circ C+273 \), \( \rho=\frac{m}{V} \) |
| Is Matter Around Us Pure? | Composition of mixtures | \( \text{Mass percentage}=\frac{\text{mass of solute}}{\text{mass of solution}}\times100 \) |
| Atoms and Molecules | Moles and molecular mass | \( n=\frac{m}{M} \), \( N=nN_A \), \( M_r=\sum \text{relative atomic masses} \) |
| Structure of the Atom | Atomic number and mass number | \( \text{neutrons}=A-Z \), shell capacity \( =2n^2 \) |
Class 10 Formula Map
| Chapter or unit | Formula focus | Key formulas or symbolic forms |
|---|---|---|
| Chemical Reactions and Equations | Balanced equations and mole ratio | Example: \( 2H_2\text{(g)}+O_2\text{(g)}\rightarrow2H_2O\text{(l)} \) |
| Acids, Bases and Salts | Hydrogen ion concentration | \( \text{pH}=-\log[H^+] \), \( \text{pH}+\text{pOH}=14 \) at \( 25^\circ\text{C} \) |
| Metals and Non-metals | Ions and charge balance | Examples: \( Na^+ \), \( Cl^- \), \( Mg^{2+} \), \( SO_4^{2-} \); neutral compound charge sum \( =0 \) |
| Carbon and Its Compounds | Homologous series | \( C_nH_{2n+2} \), \( C_nH_{2n} \), \( C_nH_{2n-2} \), \( C_nH_{2n+1}OH \) |
Class 11 Formula Map
The CBSE Class 11 Chemistry curriculum includes topics such as the importance and scope of chemistry, nature of matter, laws of chemical combination, atomic and molecular masses, mole concept, molar masses, percentage composition, stoichiometry, atomic structure, bonding, thermodynamics, equilibrium, redox reactions, organic chemistry, and hydrocarbons.
| Unit | Formula focus | Key formulas |
|---|---|---|
| Some Basic Concepts of Chemistry | Moles and stoichiometry | \( n=\frac{m}{M} \), \( N=nN_A \), \( \%=\frac{\text{part}}{\text{whole}}\times100 \) |
| Structure of Atom | Subatomic particles | \( \text{neutrons}=A-Z \), \( 2n^2 \) |
| Chemical Bonding | Valency and formal charge | \( \text{Formal charge}=V-L-\frac{B}{2} \) |
| Thermodynamics | Energy changes | \( \Delta U=q+w \), \( H=U+PV \), \( \Delta G=\Delta H-T\Delta S \) |
| Equilibrium | Equilibrium constants and pH | \( K_c=\frac{[C]^c[D]^d}{[A]^a[B]^b} \), \( K_w=[H^+][OH^-] \) |
| Redox Reactions | Oxidation number | \( \sum \text{oxidation numbers}=\text{charge} \) |
| Hydrocarbons | General formulas | \( C_nH_{2n+2} \), \( C_nH_{2n} \), \( C_nH_{2n-2} \) |
Class 12 Formula Map
| Unit | Formula focus | Key formulas |
|---|---|---|
| Solutions | Concentration and colligative properties | \( M=\frac{n}{V} \), \( x_A=\frac{n_A}{n_A+n_B} \), \( \Delta T_b=K_bm \), \( \Delta T_f=K_fm \), \( \pi=CRT \) |
| Electrochemistry | Cell potential and electrolysis | \( E_{\text{cell}}=E^\circ_{\text{cell}}-\frac{0.0591}{n}\log Q \), \( Q=It \), \( m=\frac{EIt}{F} \) |
| Chemical Kinetics | Rate and first-order reactions | \( \text{Rate}=-\frac{\Delta[A]}{\Delta t} \), \( k=\frac{2.303}{t}\log\frac{[A]_0}{[A]} \), \( t_{1/2}=\frac{0.693}{k} \) |
| Coordination Compounds | Charge and coordination number | \( \text{charge on complex}=\text{metal oxidation state}+\sum \text{ligand charges} \) |
For syllabus alignment, check the official curriculum page and the official senior secondary chemistry curriculum. For textbook reading, use the official textbook portal.
For related revision, use CBSE syllabus, Class 10 Science solutions, and Class 11 Chemistry solutions.
Most Important Chemistry Formulas for Exams
These formulas appear often because they connect directly with numerical questions, balancing, observations, and reasoning. Learn the condition of use along with each expression.
| Exam task | Formula | Use |
|---|---|---|
| Find moles | \( n=\frac{m}{M} \) | Start most stoichiometry questions. |
| Convert moles to particles | \( N=nN_A \) | Find atoms, molecules, or ions. |
| Use a balanced equation | \( \frac{n_1}{\text{coefficient}_1}=\frac{n_2}{\text{coefficient}_2} \) | Compare reactants and products by mole ratio. |
| Find empirical formula | \( \text{moles}=\frac{\text{percentage mass}}{\text{atomic mass}} \) | Convert percentage composition to simplest mole ratio. |
| Find molecular formula | \( n=\frac{\text{molar mass}}{\text{empirical formula mass}} \) | Multiply empirical formula subscripts by \( n \). |
| Find pH | \( \text{pH}=-\log[H^+] \) | Classify acidic and basic solutions. |
| Find molarity | \( M=\frac{n}{V} \) | Use litre as the volume unit. |
| Dilution | \( M_1V_1=M_2V_2 \) | Find concentration or volume after dilution. |
| Gas-law numerical | \( PV=nRT \) | Use \( T \) in Kelvin. |
| Thermodynamics | \( \Delta G=\Delta H-T\Delta S \) | Use consistent energy units. |
| Electrochemistry | \( E_{\text{cell}}=E^\circ_{\text{cell}}-\frac{0.0591}{n}\log Q \) | Use at \( 298\ \text{K} \) for log base \( 10 \) form. |
| Kinetics | \( t_{1/2}=\frac{0.693}{k} \) | For first-order reactions. |
How to Remember and Apply Chemistry Formulas
Do not learn chemistry formulas as isolated lines. Each formula belongs to a situation. The fastest way to remember it is to connect the formula with the unit and the question type.
- Read the quantity asked: mass, moles, concentration, pH, energy, rate, or cell potential.
- Write the known values with units: convert \( \text{mL} \) to \( \text{L} \), \( {}^\circ C \) to \( \text{K} \), and grams to moles where needed.
- Choose the formula by unit: if the answer unit is \( \text{mol} \), use mole relations; if it is \( \text{mol L}^{-1} \), use molarity.
- Substitute slowly: keep symbols until the last step, then insert numbers.
- Check reasonableness: mole ratio must come from a balanced equation, and Kelvin temperature cannot be negative in school gas-law problems.
Common mistakes
| Mistake | Why it is wrong | Correct habit |
|---|---|---|
| Using \( {}^\circ C \) in \( PV=nRT \) | Gas laws need absolute temperature. | Use \( K={}^\circ C+273 \). |
| Writing an unbalanced equation | Mole ratio comes only from balanced coefficients. | Balance first, calculate later. |
| Using \( \text{mL} \) directly in molarity | \( M=\frac{n}{V} \) uses litres. | Convert \( 250\ \text{mL}=0.250\ \text{L} \). |
| Mixing joule and kilojoule | \( \Delta H \) and \( T\Delta S \) must use the same energy unit. | Convert before subtracting. |
Worked Examples Using Chemistry Formulas
The examples below show the full working. Follow the same pattern in notebook answers: formula, substitution, calculation, unit, and final statement.
Example 1: Calculate moles from mass
Question: Find the number of moles in \( 18\ \text{g} \) of water. Atomic masses: \( H=1 \), \( O=16 \).
Step 1: Write the molecular formula of water as \( H_2O \).
Step 2: Find molar mass.
\[ M(H_2O)=2(1)+16=18\ \text{g mol}^{-1} \]
Step 3: Use \( n=\frac{m}{M} \).
\[ n=\frac{18\ \text{g}}{18\ \text{g mol}^{-1}}=1\ \text{mol} \]
Final answer: \( 18\ \text{g} \) of water contains \( 1\ \text{mol} \) of \( H_2O \).
Example 2: Use a balanced equation
Question: What mass of \( CO_2 \) is formed when \( 16\ \text{g} \) of methane burns completely? Reaction: \( CH_4+2O_2\rightarrow CO_2+2H_2O \). Atomic masses: \( C=12 \), \( H=1 \), \( O=16 \).
Step 1: Find molar mass of methane.
\[ M(CH_4)=12+4(1)=16\ \text{g mol}^{-1} \]
Step 2: Convert methane mass into moles.
\[ n(CH_4)=\frac{16\ \text{g}}{16\ \text{g mol}^{-1}}=1\ \text{mol} \]
Step 3: From the balanced equation, \( 1\ \text{mol} \) of \( CH_4 \) gives \( 1\ \text{mol} \) of \( CO_2 \).
Step 4: Find molar mass of \( CO_2 \).
\[ M(CO_2)=12+2(16)=44\ \text{g mol}^{-1} \]
\[ \text{mass of }CO_2=1\ \text{mol}\times44\ \text{g mol}^{-1}=44\ \text{g} \]
Final answer: \( 44\ \text{g} \) of \( CO_2 \) is formed.
Example 3: Find empirical formula
Question: A compound contains \( 40\% \) carbon, \( 6.7\% \) hydrogen, and \( 53.3\% \) oxygen by mass. Find its empirical formula. Atomic masses: \( C=12 \), \( H=1 \), \( O=16 \).
Step 1: Assume \( 100\ \text{g} \) of compound. Masses are \( C=40\ \text{g} \), \( H=6.7\ \text{g} \), and \( O=53.3\ \text{g} \).
Step 2: Convert masses into moles.
\[ n(C)=\frac{40}{12}=3.33 \]
\[ n(H)=\frac{6.7}{1}=6.7 \]
\[ n(O)=\frac{53.3}{16}=3.33 \]
Step 3: Divide by the smallest mole value.
\[ C:H:O=\frac{3.33}{3.33}:\frac{6.7}{3.33}:\frac{3.33}{3.33}=1:2:1 \]
Final answer: The empirical formula is \( CH_2O \).
Example 4: Calculate pH
Question: Find the pH of a solution with \( [H^+]=1.0\times10^{-3}\ \text{mol L}^{-1} \).
Step 1: Use \( \text{pH}=-\log[H^+] \).
\[ \text{pH}=-\log(1.0\times10^{-3}) \]
Step 2: Use \( \log(10^{-3})=-3 \).
\[ \text{pH}=-(-3)=3 \]
Final answer: The pH is \( 3 \), so the solution is acidic.
Example 5: Dilution using molarity
Question: What volume of \( 2.0\ \text{mol L}^{-1} \) acid is needed to prepare \( 250\ \text{mL} \) of \( 0.50\ \text{mol L}^{-1} \) acid?
Step 1: Use \( M_1V_1=M_2V_2 \).
\[ (2.0)V_1=(0.50)(250\ \text{mL}) \]
Step 2: Solve for \( V_1 \).
\[ V_1=\frac{0.50\times250}{2.0}=62.5\ \text{mL} \]
Final answer: \( 62.5\ \text{mL} \) of the \( 2.0\ \text{mol L}^{-1} \) acid is required.
Real-World Applications of Chemistry Formulas
Direct links to practical applications or real-world examples of formula usage help students see why formulas matter outside a notebook. The examples below connect formula, use, and reason.
| Formula | Real-world use | Why it matters |
|---|---|---|
| \( \text{pH}=-\log[H^+] \) | Testing drinking water, soil, fruit juices, and antacids. | pH tells whether a solution is acidic, neutral, or basic. |
| \( M=\frac{n}{V} \) | Preparing laboratory solutions. | Correct concentration avoids wrong titration results. |
| \( M_1V_1=M_2V_2 \) | Diluting acids and reagents. | It tells the volume of stock solution needed. |
| \( PV=nRT \) | Gas cylinders, tyres, balloons, and air-pressure problems. | It connects gas amount with pressure, volume, and temperature. |
| \( E_{\text{cell}}=E^\circ_{\text{cell}}-\frac{0.0591}{n}\log Q \) | Batteries and corrosion studies. | It shows how concentration affects voltage. |
| \( \Delta T_f=K_fm \) | Freezing-point studies and antifreeze mixtures. | It measures the lowering of freezing point by solute. |
Green Chemistry Formulas & Their Impact
Green chemistry studies how chemical processes can reduce waste, use safer materials, and improve resource use. The official senior secondary curriculum recognises green chemistry as a relevant area, so students should know the simple formulas used to compare cleaner reactions.
Important green chemistry formulas
| Measure | Formula | Impact |
|---|---|---|
| Atom economy | \( \text{Atom economy}=\frac{\text{molar mass of desired product}}{\text{total molar mass of reactants}}\times100 \) | Higher atom economy means more reactant atoms enter the useful product. |
| E-factor | \( E=\frac{\text{mass of waste}}{\text{mass of product}} \) | Lower E-factor means less waste per unit mass of product. |
| Percentage yield | \( \%\text{ yield}=\frac{\text{actual yield}}{\text{theoretical yield}}\times100 \) | Shows how much product is actually obtained. |
| Reaction mass efficiency | \( \text{RME}=\frac{\text{mass of product}}{\text{total mass of reactants}}\times100 \) | Compares product mass with reactant mass used. |
Green chemistry worked example: atom economy
Question: Find the atom economy for formation of water: \( 2H_2+O_2\rightarrow2H_2O \).
Step 1: Find the mass of desired product in the balanced equation.
\[ \text{Mass of }2H_2O=2\{2(1)+16\}=36\ \text{g} \]
Step 2: Find total mass of reactants in the balanced equation.
\[ \text{Mass of reactants}=2(2)+32=36\ \text{g} \]
Step 3: Use atom economy.
\[ \text{Atom economy}=\frac{36}{36}\times100=100\% \]
Final answer: The atom economy is \( 100\% \).
Green chemistry worked example: E-factor
Question: A process gives \( 50\ \text{kg} \) of product and \( 10\ \text{kg} \) of waste. Find the E-factor.
Step 1: Use \( E=\frac{\text{mass of waste}}{\text{mass of product}} \).
\[ E=\frac{10\ \text{kg}}{50\ \text{kg}}=0.20 \]
Final answer: The E-factor is \( 0.20 \). This means \( 0.20\ \text{kg} \) waste is formed for every \( 1\ \text{kg} \) product.
These green chemistry formulas are comparison tools. A reaction with high atom economy, good yield, and low E-factor usually uses reactants more efficiently than a reaction that produces more waste.
Frequently Asked Questions
What are the 3 types of chemical formulas?
The three common types are empirical formula, molecular formula, and structural formula. An empirical formula gives the simplest whole-number ratio, a molecular formula gives the actual number of atoms in one molecule, and a structural formula shows how atoms are connected.
What is the formula of chemistry class 10?
There is no single formula for Class 10 chemistry. Important Class 10 formulas include hydrocarbon general formulas such as \( C_nH_{2n+2} \), \( C_nH_{2n} \), and \( C_nH_{2n-2} \), charge-balance rules for ionic compounds, and the pH relation \( \text{pH}=-\log[H^+] \) as a useful higher-reference expression.
What are the basic formulas in chemistry?
Basic chemistry formulas include \( n=\frac{m}{M} \), \( N=nN_A \), \( M=\frac{n}{V} \), \( \rho=\frac{m}{V} \), \( PV=nRT \), and \( \text{pH}=-\log[H^+] \). These cover moles, particles, concentration, density, gases, and acidity.
How do you write a chemical formula?
Write the element or ion symbols, use valencies or charges, balance total positive and negative charge, and reduce the ratio if needed. For example, \( Ca^{2+} \) and \( Cl^- \) combine as \( CaCl_2 \).
What is the importance of chemistry formulas?
Chemistry formulas help students represent substances and solve questions without long descriptions. They are used to calculate mass, moles, concentration, pH, gas volume, reaction yield, cell potential, and reaction rate.
What is the difference between molecular and empirical formula?
An empirical formula shows the simplest ratio of atoms, while a molecular formula shows the actual number of atoms in a molecule. For example, glucose has molecular formula \( C_6H_{12}O_6 \), but its empirical formula is \( CH_2O \).