Hydrogen iodide, hi, is formed in an equilibrium reaction when gaseous hydrogen and iodine gas are heated together. if 20.0 g of hydrogen and 20.0 g of iodine are heated, forming 10.0 g of hydrogen iodide, what mass of hydrogen remains unreacted? a. 10.0 g hydrogen remains b. 10.9 g hydrogen remains c. 15.0 g hydrogen remains d. 19.9 g hydrogen remains.

D. 19.9 g hydrogen remains.

Explanation:

To calculate the moles, we use the equation:

a) moles of

b) moles of

According to stoichiometry :

1 mole of require 1 mole of

Thus 0.0787 moles of require= of

Thus is the limiting reagent as it limits the formation of product and acts as the excess reagent. (10.0-0.0787)= 9.92 moles of are left unreacted.

Mass of

Thus 19.9 g of remains unreacted.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.