A 100.0-mL sample of 1.00 M NaOH is mixed with 50.0 mL of 1.00 M H_2SO_4 in a la

Question

A 100.0-mL sample of 1.00 M NaOH is mixed with 50.0 mL of 1.00 M H_2SO_4 in a large Styrofoam coffee cup; the cup is fitted with a lid through which passes a calibrated thermometer. The temperature of each solution before mixing is 22.7 degree C. After adding the NaOH solution to the coffee cup and stirring the mixed solutions with the thermometer, the maximum temperature measured is 31.1 degree 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 middot degree C), and that no heat is lost to the surroundings. (a) Write a balanced chemical equation for the reaction that takes place in the Styrofoam cup. (b) Is any NaOH or H_2SO_4 left in the Styrofoam cup when the reaction is over? Yes No (c) Calculate the enthalpy change per mole of H_2SO_4 in the reaction.

Explanation / Answer

(a)

Chemical Reaction:

2 NaOH (aq.) + H2SO4 (aq.) -----------> Na2SO4 (aq.) + 2 H2O (l)

(b)

Moles of NaOH given = 1.00 * 100 / 1000 = 0.100 mol

Moles of H2SO4 given = 1.00 * 50.0 / 1000 = 0.0500 mol

From the above balanced equation,

2 mol NaOH = 1 mol H2SO4

Then, 0.100 mol NaOH = 1 * 0.100 / 2 = 0.0500 mol of H2SO4

So, no acid or base is left in the syroform cup.

(c)

we know that, q = ms (t2 - t1)

q = (100. + 50.0) * 4.184 * ( 31.1 - 22.7)

q = 5272 J

q = 5.27 kJ

Delta H = q / n

Delta H = 5.27 / 0.1 = 52.7 kJ/mol

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