Answer :
The initial temperature of the solution before the reaction occurred is; 24°C
Stoichiometry Calculations
The reaction between the hydrogen ion and hydroxide ion will be;
H⁺ + OH⁻ → H₂O
We can see that the ratio of hydrogen ions to hydroxide ions is 1:1.
Thus,
No. of moles of H⁺ = volume × concentration of H⁺
We are given;
Volume of H⁺ = 150 mL = 0.15 L
Concentration of H⁺ = 0.4 M
Thus;
No. of moles of H⁺ = 0.15 * 0.4
No. of moles of H⁺ = 0.06 mol
In a similar fashion;
No. of moles of OH⁻ = volume × concentration of OH⁻
We are given;
Volume of OH⁻ = 200 mL = 0.2 L
Concentration of OH⁻ = 0.5 M
Thus;
No. of moles of OH⁻ = 0.2 * 0.5
No. of moles of OH⁻ = 0.1 mol
Thus, the ratio of number of moles of hydrogen ions to number of moles of hydroxide ions is 0.06:0.1
Now, hydroxide ions (OH⁻) are present in excess and as such hydrogen ions (H⁺) will be the limiting reagent.
Thus;
No. of moles of water formed = No. of moles of ions = 0.06 mol.
Thus;
heat released = moles of H⁺ ions * enthalpy of neutralization(ΔH_neutr)
heat released = 0.06 mol * -62 kj/mol
heat released = 3.72 kJ = 3720 J
From energy balance, we know that;
Amount of heat released = Amount of heat absorbed by the solution
Thus;
3720 = m*c*ΔT
3720 = 350 * 4.184 * (26.5 - T)
where T is the initial temperature.
Solving for T gives T = 24°C
Read more about Stoichiometry at; https://brainly.com/question/16060223