Cerium-143 is a radioactive isotope that decays to produce praseodymium-143. The half-life for cerium-143 is approximately 33 hours. If 12.5 g cerium-143 remains from a 100-g sample, which statement is true? Select all that apply. A.
Cerium-143 decayed for 132 hours.

B.
Cerium-143 decayed for 99 hours.

C.
Four half-lives have passed.

D.
Three half-lives have passed.

E.
Cerium-143 decayed for 166 hours.

F.
Two half-lives have passed.

Which statement is usually true about the relationship between activation energy and reaction rates? low activation energy barriers result in low rates. high activation energy barriers result in low rates. low activation energy barriers result in no reaction. high activation energy barriers result in no reaction.

The two naturally occurring isotopes of chlorine are 35cl (34.969 amu, 75.77%) and 37cl (36.966 amu, 24.23%). the two naturally occurring isotopes of bromine are 79br (78.918 rm amu, 50.69%) and 81br (80.916 amu, 49.31%). chlorine and bromine combine to form bromine monochloride, brcl. 1. how many peaks will be present in a mass spectrum for brcl? the four combinations of molecule possible given these four isotopes are: 81br37cl, 81br35cl, 79br37cl, and 79br35cl. 2. what are the masses of the four different brcl molecules? express the masses using six significant figures, in decreasing numeric order (highest to lowest), separated by commas.

How many moles of cu are needed to react with 5.8 moles of agno3? cu + 2 agno3 → cu(no3)2 + 2 ag