Appendix: 1. Exponential Decay

As we already know, a drug will decay exponentially, meaning that it will decompose naturally. First, we consider the mathematics of exponential decay.

Let , be a function of time , defined as , for some positive . This equation governs the mathematics of exponential decay. We also need to define some initial condition, in other words, we need to define the value of , say .

Why is the equation called an exponential function?

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If is positive, does it make sense that there is a negative sign in the exponent? Why?

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Thus, in the Figure 1 below we see the exponential decay equation, , depicted graphically.

Figure 1: Exponential Decay (given by , with ).

What occurs to the curve as more and more time passes?

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What does this suggest regarding to the chemical substance?

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In Exponential Decay: Part 2, we will explore the effect of on the exponential decay curve.