Definitions [3]
Any reaction that involves both oxidation and reduction occurring simultaneously is called an oxidation-reduction reaction or simply a redox reaction.
or
The chemical reaction in which both oxidation and reduction occur simultaneously is called a redox reaction.
Define RQ.
Respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed in respiration over a period of time.
The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration is called Respiratory Quotient (RQ) or respiratory ratio.
Formulae [1]
\[\mathrm{RQ=\frac{Volume~ofCO_{2}~evolved}{Volume~ofO_{2}~consumed}}\]
Key Points
Redox Reactions:
- A substance that oxidises another substance (and is itself reduced) is called an oxidising agent.
- A substance that reduces another substance (and is itself oxidised) is called a reducing agent.
What is Oxidation and Reduction?
| Perspective | Oxidation | Reduction |
|---|---|---|
| In terms of oxygen | Gain of one or more O atoms | Loss of one or more O atoms |
| In terms of hydrogen | Loss of hydrogen | Gain of hydrogen |
| In terms of electropositive element | Loss of electropositive element | Gain of electropositive element |
| In terms of electronegative element | Gain of electronegative element | Loss of electronegative element |
| In terms of electrons | Loss of electrons | Gain of electrons |
| In terms of oxidation number | Increase in oxidation number | Decrease in oxidation number |
Redox in Terms of Electron Transfer:
A reaction in which electrons are lost by one substance and gained by another is called a redox reaction.
- Oxidising agent = electron acceptor
- Reducing agent = electron donor
Example:
(Hg₂²⁺ gains electrons → reduced; Sn²⁺ loses electrons → oxidised)
- Respiratory Quotient (RQ) is the ratio of volume of CO₂ evolved to volume of O₂ consumed during aerobic respiration. Formula: RQ = Volume of CO₂ evolved ÷ Volume of O₂ consumed.
- For carbohydrates - RQ = 1 (equal volumes of CO₂ and O₂); e.g., glucose: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy.
- For fats - RQ is less than 1 (more O₂ needed for oxidation); e.g., Tripalmitin: RQ = 102/145 = 0.7.
- For proteins, RQ is approximately 0.9.
- In living organisms, multiple substrates are respired together (not pure fats or proteins), so RQ is often more than 1; pure fats or proteins are never the sole respiratory substrate.
