Chapter 20, Problem 21R

To determine

The radioactivity and half-life are to be compared and contrasted.

Answer to Problem 21R

From some substance, spontaneous emission of some type of invisible rays is called radioactivity.

The time interval in which mass of radioactive substances reduced to half of its initial value is called half-life.

Explanation of Solution

Compare:

In radioactivity,it is difficult to predict exactly when the next atom will decay. Similarly, in case of half-life it is difficult to predict when half to initial value of any substance will reduced.

In both cases, after changes,substancesare more stable and, in both cases, substance is not affected by external factors.

Contrast:

In radioactivity, substance is more stable by emission of some type of rays. these rays are alpha beta and gamma rays. on the other hand, in half-life substance is more stable by reducing its mass to half of its initial value.

Conclusion:

Radioactivity and half-lifeare of two types (a) random (b) spontaneous.

Half-life is constant for a radioactive element.

Half-life and radioactivity cannot be changed by physical or chemical changes.