Question 17

Question

Chemical equations must be balanced because

a
mass can neither be created nor destroyed.

b
the mass of the reactants is always greater than the mass of the products.
c
mass is determined by a chemical reaction.
d
the mass of the products is always greater than the mass of the reactants.
Question 18
How many half-lives does it take a radioactive substance to decay until only one-eighth of the original substance remains?

a
three
b
six
c
eight
d
two

Answer 1

Question 17
Chemical equations must be balanced because
a. mass can neither be created nor destroyed.
This is based on the law of conservation of mass, which states that the total mass of the reactants must equal the total mass of the products in a chemical reaction.

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Question 18
How many half-lives does it take for a radioactive substance to decay until only one-eighth of the original substance remains?
The answer is:
a. three
This is because after one half-life, 1/2 of the original substance remains. After two half-lives, 1/4 remains. After three half-lives, 1/8 remains. (1/2 → 1/4 → 1/8).