A 100.2 mL sample of 1.00 M NaOH is mixed with 50.1 mL of 1.00 M H2SO4 in a larg

Question

A 100.2 mL sample of 1.00 M NaOH is mixed with 50.1 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. 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 32.30 °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. Calculate the enthalpy change per mole of H2SO4 in the reaction.

Explanation / Answer

moles of NaOH = 100.2 x 1 / 1000 = 0.1002

moles of H2SO4 = 50.1 x 1 / 1000 = 0.0501

mass of solution = 100.2 + 50.1 = 150.3 g

specific heat = 4.18 J / g oC

temperature rise = 32.30 - 22.25 = 10.05 oC

Q = m Cp dT

   = 150.3 x 4.184 x 10.05

   = 6320 J

delta H = - Q / n = - 6.320 / 0.0501

Enthalpy change = -126 kJ/mol

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