Chemical Equation Balancer
Balance chemical equations automatically. Enter an unbalanced equation and get the balanced version with correct coefficients.
Key features
- Automatic balancing
- Element parsing
- Coefficient calculation
- Common examples
Guide
Balancing chemical equations ensures that the number of atoms of each element is the same on both sides of the reaction, satisfying the law of conservation of mass. Matter is neither created nor destroyed in a chemical reaction. Every atom that enters as a reactant must appear in the products. This guide covers why equations need balancing, the systematic methods for doing it, types of chemical reactions, and how to handle increasingly complex equations. An unbalanced equation shows the reactants and products of a chemical reaction without correct proportions. For example, H2 + O2 -> H2O is unbalanced. The left side has 2 hydrogen atoms and 2 oxygen atoms. The right side has 2 hydrogen atoms but only 1 oxygen atom. One oxygen atom appears to vanish, which violates conservation of mass. The balanced equation is 2H2 + O2 -> 2H2O. Now the left side has 4 hydrogen and 2 oxygen atoms, and the right side also has 4 hydrogen and 2 oxygen atoms. Coefficients are the numbers placed in front of chemical formulas to balance equations. In 2H2 + O2 -> 2H2O, the coefficients are 2, 1 (implicit), and 2. Coefficients multiply every atom in the formula. 2H2O means 2 molecules of water, each containing 2 hydrogen and 1 oxygen, for a total of 4 hydrogen and 2 oxygen atoms. You never change the subscripts within a formula to balance an equation. Changing H2O to H2O2 would create a different substance (hydrogen peroxide). Balancing uses only coefficients. The inspection method (trial and error) works for simple equations. Start with the most complex molecule or the element that appears in the fewest formulas. Balance that element first, then work through the remaining elements. For Fe + O2 -> Fe2O3, iron appears once on each side and oxygen appears once on each side. Start with iron: put a 2 in front of Fe. Now 2Fe + O2 -> Fe2O3. Iron is balanced (2 on each side). Oxygen has 2 on the left and 3 on the right. Finding a common multiple: use 3O2 on the left (6 oxygen atoms) and 2Fe2O3 on the right (6 oxygen atoms). Now adjust iron: 4Fe + 3O2 -> 2Fe2O3. Check: 4 Fe left, 4 Fe right. 6 O left, 6 O right. Balanced. The algebraic method assigns variables to each coefficient and sets up a system of equations. For aFe + bO2 -> cFe2O3, the atom balance equations are: Fe: a = 2c, O: 2b = 3c. Set c = 1 (the smallest whole number for the most complex molecule). Then a = 2 and 2b = 3, so b = 3/2. To eliminate fractions, multiply all coefficients by 2: a = 4, b = 3, c = 2. Result: 4Fe + 3O2 -> 2Fe2O3. This method is systematic and works for any equation, regardless of complexity. Combustion reactions burn a substance (typically a hydrocarbon) in oxygen, producing carbon dioxide and water. The general form for hydrocarbon combustion is CxHy + O2 -> CO2 + H2O. Balance carbon first, then hydrogen, then oxygen last (because O2 is a single element and adjusting its coefficient does not affect other balances). For C3H8 + O2 -> CO2 + H2O: carbon gives 3CO2, hydrogen gives 4H2O (8 H atoms need 4 H2O), and counting oxygen on the right: 6 + 4 = 10 oxygen atoms, requiring 5O2. Balanced: C3H8 + 5O2 -> 3CO2 + 4H2O. Synthesis reactions combine two or more simpler substances into a more complex product. A + B -> AB. Example: 2Na + Cl2 -> 2NaCl. Two sodium atoms react with one chlorine molecule to form two sodium chloride formula units. These reactions are common in manufacturing, material science, and biochemistry. Decomposition reactions break a complex substance into simpler components. AB -> A + B. Example: 2H2O -> 2H2 + O2. Electrolysis of water produces hydrogen and oxygen gases. Decomposition reactions are driven by heat (thermal decomposition), electricity (electrolysis), or light (photolysis). Single replacement reactions have one element replacing another in a compound. A + BC -> AC + B. Example: Zn + 2HCl -> ZnCl2 + H2. Zinc replaces hydrogen in hydrochloric acid. Whether a replacement occurs depends on the activity series of metals, which ranks metals by their tendency to lose electrons. A more active metal displaces a less active metal from a compound. Double replacement (metathesis) reactions exchange ions between two compounds. AB + CD -> AD + CB. Example: AgNO3 + NaCl -> AgCl + NaNO3. Silver and sodium exchange partners. These reactions typically occur in aqueous solution and are driven by the formation of a precipitate (insoluble product), water, or a gas. Redox (oxidation-reduction) reactions involve the transfer of electrons between species. Oxidation is the loss of electrons; reduction is the gain of electrons. Balancing redox equations requires balancing both atoms and charges. The half-reaction method separates the overall reaction into an oxidation half-reaction and a reduction half-reaction, balances each independently (atoms and charges), then combines them so that electrons cancel. For example, in acidic solution: Fe2+ -> Fe3+ (oxidation, loses 1 electron per iron) and MnO4- -> Mn2+ (reduction, gains 5 electrons per manganese). Multiplying the iron half-reaction by 5 and combining gives 5Fe2+ + MnO4- + 8H+ -> 5Fe3+ + Mn2+ + 4H2O. Balancing redox equations in acidic solution uses H+ and H2O to balance hydrogen and oxygen atoms. In basic solution, the same process applies, then OH- ions are added to both sides to neutralize the H+ ions, converting them to water. These additional steps make basic solution balancing slightly more involved but follow the same logical framework. Polyatomic ions that appear unchanged on both sides of an equation can be balanced as a unit rather than atom by atom. In the reaction: Ca(OH)2 + H3PO4 -> Ca3(PO4)2 + H2O, the phosphate ion PO4 appears intact on both sides. Balance phosphate as a unit: 2 phosphate on the right means 2H3PO4 on the left. Balance calcium: 3 calcium on the right means 3Ca(OH)2 on the left. Count hydrogen: 6 from Ca(OH)2 + 6 from H3PO4 = 12 hydrogen atoms, needing 6H2O. Check oxygen: 6 from Ca(OH)2 + 8 from H3PO4 = 14 on the left; 8 from Ca3(PO4)2 + 6 from H2O = 14 on the right. Balanced: 3Ca(OH)2 + 2H3PO4 -> Ca3(PO4)2 + 6H2O. Stoichiometry uses balanced equations to calculate quantities in chemical reactions. The coefficients represent mole ratios. In 2H2 + O2 -> 2H2O, 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water. If you have 4 moles of hydrogen, you need 2 moles of oxygen and will produce 4 moles of water. Converting between moles and grams using molar masses allows you to calculate the mass of reactants needed and products formed. Limiting reagent problems identify which reactant runs out first, limiting the amount of product formed. If you have 10 moles of H2 and 4 moles of O2 for the reaction 2H2 + O2 -> 2H2O, the 4 moles of O2 would need 8 moles of H2 (2:1 ratio). Since you have 10 moles of H2 (more than enough), O2 is the limiting reagent. The reaction produces 8 moles of H2O with 2 moles of H2 left over. A balanced equation is the starting point for all limiting reagent calculations. Yield calculations compare the actual amount of product obtained in a laboratory or industrial process to the theoretical maximum predicted by stoichiometry. Percent yield = (actual yield / theoretical yield) x 100. Yields below 100% are normal due to side reactions, incomplete reactions, loss during transfer and purification, and measurement errors. A balanced equation provides the theoretical yield against which actual results are measured. Common mistakes when balancing equations include changing subscripts instead of coefficients, forgetting to multiply subscripts by coefficients when counting atoms, balancing hydrogen and oxygen before other elements (typically you should balance them last), and not reducing coefficients to the smallest whole numbers. The final balanced equation should have the smallest possible whole-number coefficients with no common factors. The WebRecast chemical equation balancer accepts standard chemical notation. Enter reactants and products separated by an arrow (-> or =). The tool parses the formulas, identifies all elements present, and determines the coefficients that balance the equation. It shows the balanced equation and verifies the atom count on each side. The tool handles single replacement, double replacement, combustion, synthesis, decomposition, and redox equations. All processing happens in your browser with no data sent externally.
Frequently asked questions
How does it work?
It tries coefficient combinations to balance atoms on both sides.
