A balanced equation has equal numbers of each element’s atoms on both sides. First write correct formulas, then count each element. Change coefficients in front of formulas until the counts match. Never change a subscript just to balance an equation: changing H2O into H2O2 changes water into a different substance. A coefficient multiplies every atom within the formula that follows it.
For hydrogen burning, start with H2+O2→H2O. There are two oxygen atoms on the left and one on the right. Put 2 before H2O, then 2 before H2:2H2+O2→2H2O. Both sides now contain four hydrogen atoms and two oxygen atoms. Usually report the smallest whole-number coefficients.
Example 1
Balance Mg+O2→ MgO.
Put 2 before MgO to match two oxygen atoms. This requires 2 before Mg. Balanced equation: 2Mg+O2→2MgO.
Example 2
Balance N2+H2→NH3.
Two N atoms require 2NH3. That contains six H atoms, requiring 3H2. N2+3H2→2NH3 has two N and six H atoms on each side.
Watch out:Subscripts specify the substance. Balance by changing numbers of particles using coefficients.
Balancing simple equations practice | Year 9 Science | Ascent Arcade