2.4 bromium has two naturally occurring isotopes: 79br, with an atomic weight of 78.918 amu, and 81br, with an atomic weight of 80.916 amu. if the average atomic weight for br is 79.903 amu, calculate the fraction-of-occurrences of these two isotopes.

49.3% 81Br and 50.7% 79Br or 81Br and 79BR

Step-by-step explanation:

To get the fraction-of-occurrences of the isotopes we must write the following equation. x is the isotopic abundance of 81Br, we can use 1 - x to get the isotopic abundance of 79Br.

(78.918)(1 - x) + (80.916)(x) = 79.903

78.918 - 78.918x + 80.916x = 79.903

1.998x = 0.985

x = 0.493

0.493 × 100 = 49.3% 81Br

100 - 49.3 = 50.7% 79Br

49.3% 81Br and 50.7% 79Br or 81Br and 79BR

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.