PLEASE HELP Bond energies such as those found in Table 4.4 are sometimes found by “working backward” from
heats of reaction. A reaction is carried out, and the heat absorbed or evolved is measured. From this
value and known bond energies, other bond energies can be calculated. For example, the energy
change associated with the combustion of formaldehyde (H 2 CO) is -465 KJ/mol.

H 2 CO (g) + O 2 (g)  CO 2 (g) + H 2 O (g)

a. Use the information in Table 4.4 to calculate the energy of the C=O double bond in
formaldehyde. Show all work.
b. Compare your answer with the C=O bond energy in CO 2 and speculate on why there is a
difference.

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years