Explanation:
As we know that,
[tex]H_{rxn} = \frac{-Q}{mass}[/tex]
It is given that, [tex]m_{1}[/tex] = 15 g of salt, [tex]m_{2}[/tex] = 68.8 g of ethanol
Therefore, total mass is as follows.
Total mass = [tex]m_{1} + m_{2}[/tex]
= (15 + 68.8) g
= 83.8 g
Also, change in temperature is as follows.
dT = [tex](6 - 25)^{o}C[/tex]
= [tex]-19^{o}C[/tex]
Now, the relation between heat energy, specific heat and mass is as follows.
Q = [tex]m \times C_{p} \times (dT)[/tex]
= [tex]83.8 g \times 2.440 J/g^{o}C \times (-19)^{o}C[/tex]
= -3884.968 J
Therefore, heat of the reaction is as follows.
[tex]H_{rxn} = \frac{-Q}{mass}[/tex]
= [tex]\frac{-3884.968}{15 g}[/tex]
= 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.