Calculating RQ

The RQ of a substrate can be calculated from its balanced equation for aerobic respiration:RQ = molecules of CO₂ produced ÷ molecules of O₂ usedWorked example 1: glucoseC₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂ORQ = 6 ÷ 6 = 1.0Worked example 2: a fatty acid (stearic acid)C₁₈H₃₆O₂ + 26O₂ → 18CO₂ + 18H₂ORQ = 18 ÷ 26 = 0.69Balancing the equation. If you are given only the formula, balance it yourself. Each carbon forms one CO₂, and every two hydrogens form one H₂O. Count the oxygen atoms needed in the products, subtract the oxygen atoms already in the substrate, and halve to get the number of O₂ molecules.For palmitic acid, C₁₆H₃₂O₂: products are 16CO₂ (32 O atoms) and 16H₂O (16 O atoms), so 48 O atoms are needed. The substrate provides 2, so 46 O atoms come from oxygen gas, which is 23 O₂. RQ = 16 ÷ 23 = 0.70.RQ can also be calculated from measured gas volumes: an organism that releases 18 cm³ of CO₂ and takes in 20 cm³ of O₂ has an RQ of 18 ÷ 20 = 0.90. Give RQ to two significant figures, with no units.