There are four naturally occurring isotopes of the element chromium. the relative abundance of each is 50cr - 4.345% 49.946044 amu 52cr - 83.789% 51.940508 amu 53cr - 9.501% 52.940649 amu 54cr - 2.365% 53.93880 amu find the average atomic mass of chromium. a. 52.061 amu b. 52.978 amu c. 51.996 amu d. 53.2503 amu

Answer : The correct option is, (C) 51.996 amu

Explanation :

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

As we are given that,

Mass of = 49.946044 amu

Percentage abundance of = 4.345 %

Fractional abundance of = 0.04345

Mass of = 51.940508 amu

Percentage abundance of = 83.789 %

Fractional abundance of = 0.83789

Mass of = 52.940649 amu

Percentage abundance of = 9.501 %

Fractional abundance of = 0.09501

Mass of = 53.93880 amu

Percentage abundance of = 2.365 %

Fractional abundance of = 0.02365

Now put all the given values in above formula, we get:

Therefore, the atomic weight of the element is, 51.996 amu

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.