How to Balance Redox Equations

Sulphuric Acid is reduced by Iodide ions to form Sulphur Dioxide and Iodine. Reduction Half Equation H₂SO₄ -----> SO₂ 1. Balance the species that has been oxidised or reduced. In this case the sulphur has been reduced from +6 to +4. The sulphur atoms are balanced. 2. Balance oxygen using H₂O There are 4 on LHS and 2 on RHS so add 2 H20 to the RHS H₂SO₄ ----> SO₂ + 2H₂O 3. Balance hydrogen atoms (H+) There are 2 on LHS and 4 on RHS so add 2H+ to LHS H₂SO₄ + 2H⁺ ----> S

Limiting Reagents

If you have worked out the MOLES of two reactants then the limiting reagent is the one with less moles. Sorted? Well, it depends. If the reactants are in a 1:1 ratio then the above is true. But if the ratio is not equal then I'm afraid it's a bit more complicated. Let's say reactants A and B have a ratio of 2:1 in the balanced equation. If we have 0.020 moles of A and 0.015 moles of B which is the limiting reagent? If we start with A we can see from the ratio that 0.02 moles