Rate of Reaction

The rate of reaction is how fast a chemical reaction will proceed. We can express the rate of reaction as either the disappearance of reactants per unit time, or we can express it as the appearances of product per unit time. Either way, the units we’re going to use is concentration per time, so it’s going to look like this.

This is molarity over second, so it’s the concentration (or the molarity) per seconds (or per time). Now, reaction rates can be distinguished between an average rate and an instantaneous rate. If we have a reaction like this, the way we would find the average rate is by looking at the change in product divided by change in time, or by looking at the change of reactant divided by change in time.

I’m saying it’s equal because they’re going to equal each other because if you take a look at an average then the rate of reactant decreasing (or disappearing) is going to equal the rate of products appearing because that’s how the reaction has to work.

If something’s disappearing over here, it means it’s appearing over here; and if something’s appearing over here, it means something’s disappearing over here. Now in contrast, the instantaneous rate is the rate of reaction at a specified time, so it’s not an average it’s at a specified time.

The instantaneous reaction is determined by examining a graph. The graph is going to have time over here on the x-axis, and then on the y-axis it is either going to have the appearance of product or the disappearance of reactant (so it’s going to be the appearance of product or the disappearance of reactant, versus time).

We’re going to take a look at that graph and then at any specified time the instantaneous rate of reaction is going to be the slope of the line tangent to the curve at that specified time. Again, the rate of reaction is how fast a chemical reaction will proceed.