Question

. The heat released when one mole of water is formed from the elements is 1,198 kJ. An experiment was conducted that permitted water to form in this manner, and the heat was contained in 2.0 liters of water. The water temperature before the reaction was 34.5C, and after the reaction it had risen to 52.0C. How many moles of oxygen did react?

Answer 1

No. of moles of oxygen = 0.1223 mol

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Specific heat capacity of water = 4.186 J/g.oC

Volume of water = 2.0 L

Density of water = 1 g/mL

Mass of water = 2000 mL x 1g/mL = 2000 g

Temperature (initial) = 34.5 oC

Temperature (final) = 52.0 oC

delta T = T(final) - T(initial) = 52.0-34.5 = 17.5 oC

heat produced in the reaction is = heat gained by water

Q = m c delta T,

Q (water) = 2000 g x 4.186 J/g.oC x 17.5 oC = 146510 J = 146.51 kJ

Heat released by 1 mole of water = 1198 kJ

No. of moles of water formed = 146.51 kJ / 1198 kJ = 0.1223 mol.

In the formation of water 1 mole of O reacts with 2 moles of H and form 1 moles of H2O,

So no. of moles of oxygen = 0.1223 mol