Question

solve for the following enthalpy changes
NaOH(s) /Na+(aq) + OH-(aq)

When 5.13g NaOH is dissolved in 200.0ml of water, the temperature increases 6.63 degrees celsius

Answer 1

NaOH moles = mass / Molar mass of NaOH

          = 5.13 g / 40g/mol   = 0.12825

water mass = volume of water x density = 200 ml x 1g/ml = 200 g

solution mass = water mass + NaoH mass = 200+5.13 = 205.13 g

Heat absorbed by solution = specific heat of solution x mass of solution x temperature rise

Heat absorbed = 4.184 J/gK x 205.13 g x 6.63 C

        = 5690.3 J = 5.69 KJ

Enthalphy of dissolution = heat released / moles of NaoH   =- 5.69 / 0.12825

   = - 44.37 KJ/mol ( -ve sign indicates heat released)