Question
22. The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?
a
50 g
b
100 g
c
75 g
d
25 g
24. Chemical equations must be balanced because
a
mass can neither be created nor destroyed.
b
mass is determined by a chemical reaction.
c
the mass of the reactants is always greater than the mass of the products.
d
the mass of the products is always greater than the mass of the reactants.
a
50 g
b
100 g
c
75 g
d
25 g
24. Chemical equations must be balanced because
a
mass can neither be created nor destroyed.
b
mass is determined by a chemical reaction.
c
the mass of the reactants is always greater than the mass of the products.
d
the mass of the products is always greater than the mass of the reactants.
Answers
GPT-4o mini
For question 22, the half-life of element X is 5 days, meaning that every 5 days, half of the substance decays. After 10 days, which is two half-lives, the remaining amount can be calculated as follows:
1. After the first 5 days (1 half-life), 100 g becomes 50 g.
2. After the second 5 days (2 half-lives), 50 g becomes 25 g.
Thus, after 10 days have passed, **25 g** of element X remains. The answer is:
**d) 25 g.**
For question 24, the reason chemical equations must be balanced is:
a) mass can neither be created nor destroyed.
This statement is based on the law of conservation of mass, which states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products. Therefore, the correct answer is:
**a) mass can neither be created nor destroyed.**
1. After the first 5 days (1 half-life), 100 g becomes 50 g.
2. After the second 5 days (2 half-lives), 50 g becomes 25 g.
Thus, after 10 days have passed, **25 g** of element X remains. The answer is:
**d) 25 g.**
For question 24, the reason chemical equations must be balanced is:
a) mass can neither be created nor destroyed.
This statement is based on the law of conservation of mass, which states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products. Therefore, the correct answer is:
**a) mass can neither be created nor destroyed.**