Answer:
Density is 2.7 grams
Explanation:
formula for density is p= mass over volume [p being density]. So all you have to do is divide
The reaction will be: FeBr2 + K --> KBr + Fe
Balancing gives: FeBr2 + 2K --> 2KBr + Fe
The molar mass of FeBr2 is 55.85 + 2*79.9 = 215.65 g/mol.
We divide 40 g / 215.65 g/mol = 0.185 mol FeBr2
Based on stoichiometry:
(0.185 mol FeBr2)(2 mol KBr/1 mol FeBr2) = 0.370 mol KBr
Answer : The number of moles of ethane required will be 0.166 mole.
Explanation :
First we have to calculate the heat absorbed by water.

where,
q = heat absorbed = ?
m = mass of water = 851 g
c = specific heat of water = 
= final temperature = 
= initial temperature = 
Now put all the given values in the above formula, we get:

(1 kJ = 1000 J)
Now we have to calculate the moles of ethane required.

where,
= enthalpy of combustion of ethane = 1560.7 kJ/mol (standard value)
q = heat absorbed = 259.67 kJ
n = number of moles of ethane = ?



Therefore, the number of moles of ethane required will be 0.166 mole.