[polymerase]

Is this chemical equation correct?

C₇H₆O₂ + NaHCO₂ (right arrow) C₇H₅O₂Na + H₂O + CO₂

[Borek]

Check if oxygen is balanced.

Check sodium bicarbonate formula.

[polymerase]

Check if oxygen is balanced.

Check sodium bicarbonate formula.

C₇H₆O₂ + NaHCO₃ (right arrow) C₇H₅O₂Na + H₂O + CO₂


as well, should reactions like these have double arrow(one foward one back) or just forward

[Yggdrasil]

In this case, having only a forward arrow is appropriate.  CO₂ is evolved as a gas, meaning that it goes away from the solution before the backward reaction has a chance to occur.

[Borek]

C₇H₆O₂ + NaHCO₃ (right arrow) C₇H₅O₂Na + H₂O + CO₂

Seems OK.

as well, should reactions like these have double arrow(one foward one back) or just forward

Define "like these". CO₂ is a gas, so it leaves reaction mixture, but in general you have to compare pKa of all acids present.

Ygg beat me as I was moving furniture in the meantime I am repeating part of his answer, but let it be.