In the reaction, 2h2 o2 --> 2h2o, how many hydrogen molecules are needed to produce two water molecules? a. 1b. 2c. 3d. 4

b. 2

There are necessary 2 hydrogen molecules to produce 2 water molecules.

Explanation:

The balanced equation is already given:

So, 2 molecules of diatomic hydrogen react with 1 molecule of diatomic oxygen to obtain 2 water molecules.

As you can see in the attached image, the 2 molecules of diatomic hydrogen have 2 hydrogen atoms each (i.e. 4 hydrogen atoms), the molecule of diatomic oxygen has 2 oxygen atoms and the 2 water molecules have 2 hydrogen atoms and 1 oxygen atom each (i.e. 4 hydrogen atoms and 2 oxygen atoms)

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

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

that's it!

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~ trueboss72