Question

How much heat is evolved in converting 1.00 mol of steam at 135.0 ∘C to ice at -55.0 ∘C? The heat capacity of steam is 2.01 J/(g⋅∘C) and of ice is 2.09 J/(g⋅∘C).

Answer 1

Solution :-

When steam changes to ice at -55.0 C then it gives off heat

calculating heat lost by steam when it chages to 135 to 100 C

q1 = n* c*delta T

= 1 mol * (2.01 J per g C * 18.0148 g/ 1 mol ) * (35 C)

= 1267.3 J

1267.3 J* 1 kJ / 1000 J = 1.267 kJ

Amount of heat given when steam condense to liquid

q2 = heat of vap * 1 mol

q2 = 40.7 kJ per mol * 1 mol

q2 = 40.7 kJ

amount of heat loss by water

q3= m*c*delta T

= 18.0148 g * 4.184 J per g C * 100 C

=7537 J

7537 J * 1 kJ /1000 J = 7.537 kJ

Amount of heat given in freezing

Q4= deltaH fus * n

= 6.01 kJ per mol * 1 mol

= 6.01 kJ

Amount of heat given by ice

q5 = m*c*delta T

    = 18.0148 g * 2.09 J per g C * 55 C

    = 2071 J

2071 J * 1 kJ / 1000 J = 2.071 kJ

Now lets calculate the total amount of heat given off

Qtotal = q1 +q2 +q3 +q4 +q5

           = 1.267 kJ + 40.7 kJ + 7.537 kJ + 6.01 kJ + 2.071 kJ

          = 57.6 kJ

So the total amount of heat evolved = 57.6 kJ