A 99.2 mL sample of 1.00 M NaOH is mixed with 49.6 mL of 1.00 M H2SO4 in a large Styrofoam coffee cup; the cup is fitted with a lid through which passes a calibrated thermometer.

Question

The temperature of each solution before mixing is 22.25 °C. After adding the NaOH solution to the coffee cup and stirring the mixed solutions with the thermometer, the maximum temperature measured is 32.70 °C. Assume that the density of the mixed solutions is 1.00 g/mL, that the specific heat of the mixed solutions is 4.18 J/(g·°C), and that no heat is lost to the surroundings.

Write a balanced chemical equation for the reaction that takes place in the Styrofoam cup. Remember to include phases in the balanced chemical equation.

Calculate the enthalpy change per mole of H2SO4 in the reaction. (answer is in kj/mol)

Answer 1

H₂SO₄(aq) + 2NaOH(aq) ==> Na₂SO₄(aq) + 2H₂O(l) ... balanced equation

To find the enthalpy change per mole, we need to find the heat generated by the reaction and then convert to to heat on a per mole bases.

q = mC∆T

q = heat = ?

m = mass = 99.2 ml + 49.6 ml = 148.8 ml x 1 g/ml = 148.8 g

C = specific heat = 4.18 J/gº

∆T = change in temperature = 32.70º - 22.25º = 10.45º

q = (148.8 g)(4.18 J/gº)(10.45º)

q = 6500. J = 6.500 kJ = enthalpy of reaction

To find ∆H/mol we need to find moles of H2SO4 or moles NaOH

moles H2SO4 = 0.0496 L x 1.0 mol /L = 0.0496 moles H2SO4

moles NaOH = 0.0992 L x 1.0 mol/L = 0.0992 moles NaOH / 2 mol per mol H2SO4 = 0.0496 mol NaOH

∆H/mol = 6.500 kJ / 0.0496 mol = 131.0 kJ/mol