· Exponential function
· Natural exponential function
· Exponential decay
Equation 
· y = a^{x} · Output equals a constant to the power of the input 
Graph 
Runaway curve

Equation 
· y=Ae^{x} = δy/δx (where e = 2.718281828…) · i.e. rate of change of Y is proportional to amount of Y 
Graphs 

Use 
Used to model timedependent exponential processes · Drug metabolism · Alveolar filling · Preoxygenation · Radioactive decay 
Equation 
N = N_{0}e^{kt} Where · N = amount of isotope · N_{0} = amount of isotope at t=0 
Graph 

Rate constant (k) 
· Proportion of isotopes decaying per unit time, had the initial rate of decay continued · Units: min^{1} 
Time constant (τ) 
· Time taken for completion had the initial rate of decay continued · τ = 1/k · Units: minutes · ~95% completion at 3 x τ 
Half life (t_{1/2}) 
· Time taken for 50% decay · t_{1/2} = τ x log_{e}2 · ~97% completion = 5 x t_{1/2} 
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