Half Life | MCQs

Explanation

Decaying involves the breakdown of organic matter into simpler substances through chemical reactions.

It alters the original composition of the material, which is a hallmark of a chemical change.

Explanation

To find the time it takes to decay 75% of the initial amount, we need to find the time it takes for 25% of the initial amount to remain.

Since the half-life is 4.5 × 10^9 years, after one half-life, 50% of the initial amount remains.

After two half-lives, 25% of the initial amount remains (50% of 50%).

Therefore, the time it takes to decay 75% of the initial amount is:

2 × half-life = 2 × 4.5 × 10^9 years = 9 × 10^9 years

Explanation

The substance reduces to (1/16) = (1/2)^4 of its original mass.  

This means 4 half-lives = 40 days  

So, 1 half-life = 40 / 4 = 10 days  

Explanation

 Half-life definition:

The half-life of a radioactive substance is the time it takes for half of the atoms in a sample to decay. 

This decay process is inherent to the specific nucleus of the atom, meaning the half-life is a property of the substance itself and is independent of factors like the amount present or how old the sample is. 

Explanation

When a radioactive element undergoes decay, the number of atoms decreases by half every half-life. So, after "n" half-lives, the number of atoms left behind is:

No × (1/2)^n

Where:

No = initial number of atoms

n = number of half-lives

This is because the decay process follows a geometric progression with a common ratio of 1/2.

So, after "n" half-lives, the number of atoms left is (1/2)^n times the initial number, which is:

(1/2)^n No

Explanation

Since the reaction order is second, the formula for t1/2=k−1[A]−10.

This means that the half-life of the reaction is 0.0259 seconds

while

For a first-order reaction, t1/2 is independent of the initial concentration of reactants.

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The rate constant of a zero-order reaction is equal to the rate of reaction.

R: t1/2 for zero order reaction is directly proportional to the initial concentration

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A third-order reaction is a reaction in which the rate is directly proportional to the concentration of three reacting molecules.