How much of a sample remains after five half-lives have occurred?
a. 1/5 of the original sample
b. 1/25 of the original sample
c. 1/32 of the original sample
d. 1/64 of the original sample

1/32 of the original sample

Explanation:

The half life of a material refers to the time it takes for the material to decay to half of the original amount present.

If N=1/2 No after one half life, then after five half lives;

N= (1/2)^5No

N= 1/32 No hence the answer

Note N= amount of radioactive substance present at a time (t)

No= initial amount of radioactive substance present at t=0

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"