Indium (in) is made up of 95.7% 115in and 4.3% 113in. the atomic mass of 113in is 112.904 amu. the atomic mass of 115in is 114.904 amu. what is the average atomic mass of a sample of indium?

amu In = 114.818 amu

Explanation:

Indium (In):

∴ 95.7% 115In

∴ 4.3% 113In

∴ atomic mass 113In = 112.904 amu

∴ atomic mass 115In = 114.904 amu

average atomic mass (In):

⇒ amu In = (0.957)(114.904 amu) + (0.043)(112.902 amu)

⇒ amu In = 109.963 amu + 4.855 amu

⇒ amu In = 114.818 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.