Respuesta :
ΔH for the process is -252.3 cal/mol or -1056 j/mol.
What is Enthalpy of Solution ?
A solid salt compound dissociates in liquid water to form an aqueous solution of its constituent ions.
This is a chemical reaction, with the required heat change at constant pressure termed the enthalpy of solution.
If this value is positive, then the final prepared solution will have a lower temperature than the starting pure solvent.
Conversely, a negative enthalpy value results in a solution temperature that is higher than the starting solvent temperature.
It is given that
NaOH (s) → Na (aq) + OH (aq)
mass of NaOH is 16.9 g
mass of water = 70 g
ΔT = 86.6-22.4 °C = 64.2 °C
q = m × Cg × ΔT
q = amount of energy released or absorbed
m = mass
Cg = specific heat capacity
ΔT = change in temperature
n = m ÷ M
n = moles of solute
m = mass of solute
M = molar mass of solute
ΔHsoln = q ÷ n
ΔHsoln = molar enthalpy (heat) of solution
q = amount of energy (heat) released or absorbed
n = moles of solute
Cg= 1 cal/gm/°C
Now substituting the values in the equation
q = m × Cg × ΔT
q = 16.9 * 1 * 64.2
q = 1085 cal
n = m ÷ M
M= 70/18=3.9
n=16.9/3.9
n=4.3
ΔH = q ÷ n
ΔH =1085 /4.3
ΔH= -252.3 cal/mol or -1056 j/mol
Therefore ΔH for the process
NaOH(s) → Na(aq) + OH(aq)
is -252.3 cal/mol or -1056 j/mol
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