Question

When 15.0 g of a salt was dissolved in 68.8 g of ethyl alcohol, the temperature of the solution decreased from 25.0 °C to 6.0 °C. The specific heat capacity for ethyl alcohol is 2.440 J/g°C. Calculate the heat of reaction (∆H) in units of kJ/g. (Equation 1 and Equation 2 will be helpful.)

Answer 1

Explanation:

As we know that,

        $H_{rxn} = \frac{-Q}{mass}$

It is given that, $m_{1}$ = 15 g of salt,   $m_{2}$ = 68.8 g of ethanol

Therefore, total mass is as follows.

    Total mass = $m_{1} + m_{2}$

                       = (15 + 68.8) g

                       = 83.8  g

Also, change in temperature is as follows.

              dT = $(6 - 25)^{o}C$

                    = $-19^{o}C$

Now, the relation between heat energy, specific heat and mass is as follows.

               Q = $m \times C_{p} \times (dT)$

                   = $83.8 g \times 2.440 J/g^{o}C \times (-19)^{o}C$

                   = -3884.968 J

Therefore, heat of the reaction is as follows.

            $H_{rxn} = \frac{-Q}{mass}$

                       = $\frac{-3884.968}{15 g}$

                      = 258.99 J/g

As 1 J = 0.001 kJ. So, heat of reaction in kJ is 0.2589 kJ/g.

Thus, we can conclude that heat of reaction is 0.2589 kJ/g.