Question

Calculate the heat energy releashed when 12.5 g of liquid mercury at 25 degrees Celsius is converted to solid mercury at its melting point.

Answer 1

The answer is -254J

Explanation

Heat of fusion of mercury = 2.29kJ/mol

specific heat of mercury = 0.1395J/g℃

There are two energy calculations involved

1. Energy released when cooling of liguid mercury at 25℃ to its melting point temperature ( -38.83℃), q₁

q = m × ∆T × C

where,

m = mass of mercury , 12.5g

∆T = Temperature difference , -63.83℃

C = heat capacity of mercury, 0.1395J/g℃

q = 12.5g × (-63.83℃) × 0.1395J/g℃

= - 111.3J

  

_{2. Heat released when liquid mercury freeze at it's freezing point,} q₂

  ∆H_fus = 2.29kJ /mol

molar mass of mercury = 200.592g/mol

So,

∆H_fus for 12.5g of mercury = (2.29kJ/200.592g)×12.5g =0.1427kJ = 142.7J

So,

q_{2 = - 142.7J}

_Therefore,

Total energy released= - ( q_{1 +} q₂)

= - ( 111.3J + 142.7J )

= - 254J