<u>Answer:</u> The molar mass of the mystery element is 111.27 g/mol
<u>Explanation:</u>
To calculate the heat absorbed by the calorimeter, we use the equation:
where,
q = heat absorbed
c = heat capacity of calorimeter = 1650 J/°C
= change in temperature =
Putting values in above equation, we get:
Heat absorbed by the calorimeter will be equal to the heat released by the reaction.
<u>Sign convention of heat:</u>
When heat is absorbed, the sign of heat is taken to be positive and when heat is released, the sign of heat is taken to be negative.
To calculate the number of moles of the mystery molecule, we use the equation:
where,
q = amount of heat released = -4191 J
n = number of moles = ? moles
= enthalpy change of the reaction = -2960 kJ/mol = -2960000 J/mol (Conversion factor = 1 kJ = 1000 J)
Putting values in above equation, we get:
To calculate the number of moles, we use the equation:
Given mass of mystery molecule = 0.158 g
Moles of mystery molecule = 0.00142 mol
Putting values in above equation, we get:
Hence, the molar mass of the mystery element is 111.27 g/mol