One of Dalton's hypotheses about matter was that the smallest "unit" (the atom) cannot be subdivided, created or destroyed . . . this was based on an existing concept which is now known as the . . . . it is the basis for balancing chemical equations and performing much of the math in chemistry. In fact, the word "atom" comes from the Greek atomos meaning indivisible and uncuttable. It is this law that affords chemists and chemistry students the exhilarating pleasure of balancing chemical equations.
Simply make the mass of the . . . . compounds formed during a reaction. Products are located to the right of the reaction arrow (→) equal to the mass of the . . . . compounds broken apart during a reaction. Reactants are located to the left of the reaction arrow (→) and the equation will be balanced. In practice, it is actually easier to make the type and number of reactant atoms equal to the type and number of the product atoms. To do this you will need to apply some previously learned skills:
- properly adding the number of atoms present in a chemical formula (Section 2.4)
- writing the chemical formula from a compound's name (Section 2.6)
While balancing chemical equations is mostly "trial and error", the following steps will reduce the number of "errors" you will encounter:
- Never change a compound's formula to balance an equation . . . . only a reactant's (or product's) coefficient is changed.
- Identify the most complex substance and choose an element in it that appears in only one other compound. Adjust the coefficients to obtain the same number of atoms of this element on both sides.
- Balance . . . . ions containing more than one element . . . NH4+, C2H3O2-, MnO4-, CO32-, CrO42-, SO42-, PO43-, etc. (if present on both sides of the chemical equation) as a unit.
- If a reactant or product is an element, balance it last.
- Balance the remaining atoms . . . end with the least complex substance . . . use fractional coefficients if necessary.
- Convert fractional coefficients to a whole number by multiplying ALL coefficients by the denominator of the fraction.
- Check your work by counting the atoms of each type on both sides of the equation.
Chem21Labs has developed an interactive equation grader that gives immediate feedback on a submitted equation. The image below shows all the "parts" of a balanced equation: coefficient, formula, charge, and state of matter. While the coefficient and formula are required for a balanced equation, the other two (charge and state of matter) are optional. If an optional property is required, the drop-down box will be visible. The animation to the right gives additional details about the parts of a balanced equation . . . . mouse over the coefficient, formula, charge and state of matter to reveal this information.
Ionic Equation - consider the reaction between HCl and NaOH. There are three types of chemical equations: molecular, ionic and net ionic. The molecular equation for the reaction between HCl and NaOH is . . . .
HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)
If a . . . . the number written to the left of a formula that balances a chemical equation. is "1" it is not written. The ionic equation breaks ionic compounds that are aqueous (they have an (aq) after the formula) into their ions as shown below:
H+(aq) + Cl–(aq) + Na+(aq) + OH–(aq) → H2O(l) + Cl–(aq) + Na+(aq)
There are four reactants and three products in the Ionic equation. The Net Ionic Equation is a simplified version of the ionic equation where . . . . ions that are present in exactly the same quantity and state on both the reactant and product side of an ionic equation. are removed.
H+(aq) + Cl–(aq) + Na+(aq) + OH–(aq) → H2O(l) + Cl–(aq) + Na+(aq)
H+(aq) + OH–(aq) → H2O(l) (net ionic equation)
What's the purpose of net ionic equations? They show the "players" in a chemical reaction and help chemists organize reactions. For example, the net ionic equation between hydrobromic acid and potassium hydroxide is also H+(aq) + OH–(aq) → H2O(l)
H+(aq) + Br–(aq) + K+(aq) + OH–(aq) → H2O(l) + Br–(aq) + K+(aq)
H+(aq) + OH–(aq) → H2O(l) (net ionic equation)
Acid + Base → Salt + Water
H2SO4(aq) + 2 CsOH(aq) → Cs2SO4(aq) + 2 H2O(l)
H+(aq) + OH–(aq) → H2O(l)
(net ionic equation)
In fact, any of the acids (below) will react with any of the bases (below) in an acid‑base reaction to form a salt + water . . . . sulfuric acid and cesium hydroxide provide a representative example.
Acid: HF, HCl, HBr, HI, HC2H3O2, HNO3, H2SO4, H3PO4, etc.
Base: LiOH, NaOH, KOH, CsOH, RbOH, Mg(OH)2, Ca(OH)2, Ba(OH)2, Sr(OH)2, Al(OH)3, etc.
With just the acids and bases listed, there are 8 × 10 (80) acid-base reactions that share the same net ionic equation.