The molar mass of potassium chloride is 74.5513g/mol, and the molar mass of potassium bromide is 119.002g/mol. You first need to find how many moles are in the given sample, so you divide the mass by the molar mass of potassium bromide. You don’t necessarily need to convert the mole ratio, since both the potassium chloride and potassium bromide have 2 moles in the chemical equation. Lastly, you multiply the moles at this point by the molar mass of potassium chloride, and you get your final answer.
<span>The average molar bond enthalpy of the carbon-hydrogen bond in a CH4 molecule is 416 KJ/mol.
(+716.7 + (4 x 218) - (- 74.6) ) / 4
= + 1663.3 / 4
= 416</span>