Definitions [3]
Any reaction that involves both oxidation and reduction occurring simultaneously is called an oxidation-reduction reaction or simply 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 respiration.
- For carbohydrate respiration, RQ = 1.
- For fats, RQ is less than 1.
- For proteins, RQ is approximately 0.9.
- Respiration helps maintain the balance between CO₂ and O₂ in the atmosphere.
- Respiration provides energy required for synthesis of biomolecules and other cellular activities.
