v ordem 1 (v = k[A])
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
This calculator determines the rate of a first-order chemical reaction, where the rate depends linearly on the concentration of a single reactant. The formula used is v = k[A], where 'v' is the reaction rate, 'k' is the rate constant, and '[A]' is the reactant concentration. It is suitable for processes like substance decomposition or enzyme kinetics, where the reaction order is experimentally confirmed.
To use the tool, input the rate constant (k) and the reactant concentration ([A]). The result displays the instantaneous reaction rate. Ensure the reaction is indeed first-order, as this model does not apply to other orders. Avoid negative or zero values, since concentrations cannot be negative.
Common examples include the decomposition of N₂O₅ under controlled conditions or radioactive decay kinetics. Additional precautions include verifying that temperature and pressure were constant during experiments, as 'k' depends on these factors. For more complex reactions (zero or second order), other calculators are required.
Frequently asked questions
How does the first-order reaction formula work?
The formula v = k[A] means the rate is proportional to the rate constant multiplied by the reactant concentration. It applies only to first-order reactions.
When should this calculator be used?
For chemical processes where the reaction order has been experimentally confirmed as first-order, like pure substance decomposition or simple enzyme kinetics.
What if the concentration is given in different units?
Convert units to the same scale before using the calculator. The rate constant k must be in compatible units with concentration and time (e.g., s⁻¹).
Why might the result vary with the same inputs?
If the reaction isn't strictly first-order or if temperature/pressure changes, the calculation may not match experimental results.