Question

23.6 g of calcium chloride (110.98) is dissolved in water in a calorimeter. T rose from 25.0°C to 38.7°C. Heat capacity of solution & calorimeter = 1258 J/°C. What is enthalpy change when 1 mol CaCl2 dissolves?

Answer 1

Answer:

Enthalpy Change when 1 mole CaCl₂ dissolves

= - 81.13 kj/mole

Explanation:

Given information

    Mass of CaCl₂ = 23.6 g

Temperature changes from 25.0°C to 38.7°C

Heat capacity of solution & calorimeter (C) = 1258 J/°C

We know               Q = C x ΔT

                   ⇒ Heat released =  1258 x (38.7 - 25)

                                                = 1.7234 x 10⁴ J

                                                = 17.2 Kilo-joule

Thus 23.6 g is equivalent to 1.7234 x 10⁴ J or 17.2 Kilo-joule  of heat energy

Molar mass of calcium chloride (110.98)

$Mole =\frac{Mass}{Molecular mass} = \frac{23.6}{110.98} =0.212 mole$

Enthalpy Change when 1 mole CaCl₂ dissolves

                      = $\frac{-17.2}{0.212} kj/mol = -81.13 kj/mole$