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We have been doing experiments on the rate of photosynthesis to find out the importance of $\ce{CO2}$ and we used $\ce{KHCO3}$ in one beaker and found that the plant kept in that beaker produced greater amount of oxygen that those without it. Sources say that $\ce{KHCO3}$ acts as a source of $\ce{CO2}$ but I'm not sure of it. What is the reaction taking place to produce $\ce{CO2}$?

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    $\begingroup$ $\ce{HCO3-(aq) + H2O(l) <=> H2CO3(aq) + OH-(aq) <=> H2O(l) + CO2(aq) + OH-(aq)}$ Now, that does not mean that if you dissolve $\ce{KHCO3}$ in water, it will immediately decompose and you get bubbles of $\ce{CO2}$. It is just that the plant is using the $\ce{CO2}$, so that pulls the equilibrium over, Le Chatelier's principle, etc. $\endgroup$ – orthocresol Sep 26 '16 at 18:23
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    $\begingroup$ or as I like to think of it: $$\ce{HCO3^-(aq) + H2O(l) <=> H2CO3(aq) + OH^-}$$ $$\ce{H2CO3(aq) <=> H2O(l) + CO2(aq)}$$ $\endgroup$ – MaxW Sep 26 '16 at 18:27
  • $\begingroup$ I think one of the crucial steps is also $\ce{CO2 (aq) <=>> CO2 ^ }$ since plants are absorbing carbon dioxide from the air (mostly). $\endgroup$ – Martin - マーチン Nov 15 '16 at 13:14
  • $\begingroup$ @Martin-マーチン The transfer of atmospheric CO2 was cut off before the readings were taken. $\endgroup$ – Tyto alba Feb 16 '17 at 15:45
  • $\begingroup$ I was never implying that, if you read correctly, I am saying that the carbon dioxide needs to diffuse out of the solution before the plants can absorb it. $\endgroup$ – Martin - マーチン Feb 16 '17 at 16:37
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Compiling the comments by Max and orthocresol:

What is the reaction taking place to produce CO2?

$$\ce{HCO3− (aq) + H2O (l) <=> H2CO3 (aq) + OH− (aq) <=> H2O (l) + CO2 (aq) + OH−(aq)}$$

or \begin{align} \ce{HCO3− (aq) + H2O (l) &<=> H2CO3 (aq) + OH−}\\ \ce{H2CO3 (aq) &<=> H2O (l) + CO2 (aq)} \end{align}

$\ce{KHCO3}$ does not readily decompose into $\ce{CO2}$ when dissolved in water. It is just that the plant is using the $\ce{CO2}$, so that pulls the equilibrium over, Le Chatelier's principle.

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I am not sure about the previous answers but when KHCO3 reacts with water it forms a complex [K(H20)6]+ and bicarbonate ion. And hence no Carbon dioxide is formed.

But if Potassium carbonate decomposes between 373K and 393K it forms CO2.

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