Question

A substance decays so that the amount a of the substance left at time t is given by: a = a0 ∙ (0.8)t where a0 is the original amount of the substance. what is the half-life (the amount of time that it takes to decay to half the original amount) of this substance rounded to the nearest tenth of a year?

Answer 1

The half-life of the substance is 3.106 years.

What is the formula for exponential decay?

• The exponential decline, which is a rapid reduction over time, can be calculated with the use of the exponential decay formula.
• The exponential decay formula is used to determine population decay, half-life, radioactivity decay, and other phenomena.
• The general form is F(x) = a.

Here,

a = the initial amount of substance

1-r is the decay rate

x = time span

The equation is given in its correct form as follows:

a = $a_{0}$×$(0.8)^{t}$

As this is an exponential decay of a first order reaction, t is an exponent of 0.8.

Now let's figure out the half life. Since the amount left is half of the initial amount at time t, that is when:

a = 0.5 a0

Substituting this into the equation:

0.5$a_{0}$ = $a_{0}$×$(0.8)^{t}$

0.5 = $(0.8)^{t}$

taking log on both sides

t log 0.8 = log 0.5

t = log 0.5/log 0.8

t = 3.106 years

The half-life of the substance is 3.106 years.

To learn more about exponential decay formula visit:

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