What variable always appears in any reaction rate calculation? Would that be time?~seconds/s?
The variable that always appears in any reaction rate calculation is indeed time, usually denoted as "t". The reaction rate is a measure of how quickly reactants are being consumed or products are being formed over time. The rate is typically expressed as a change in concentration (or pressure) per unit time.
To determine the reaction rate, you need to know the change in concentration of a reactant or product, as well as the corresponding time interval. Here's a simple example to illustrate:
Let's say we have a reaction: A + 2B → C. The rate of this reaction can be determined by measuring the change in concentration of A (Δ[A]) or C (Δ[C]) over a certain time period (Δt).
To calculate the reaction rate, you divide the change in concentration by the corresponding time interval:
Rate = Δ[A] / Δt or Rate = Δ[C] / Δt
The units of reaction rate can vary depending on the orders of the reactants in the balanced equation. In this case, since we're looking at the change in concentration per unit time, the unit of the rate would be typically expressed as mol/(L·s) or M/s.
So, to summarize, while time is a critical variable in any reaction rate calculation, the specific concentration change over time is also required to determine the rate accurately.