How much heat (in kilojoules) is evolved or absorbed in the reaction of 1.90g of Na with H2O?

2Na (s) + 2H₂O (l) - > H2 (g) deltH = - 368.4KJ.

The heat of the reaction is an extensive property: it is proportional to the quantity of the quantity that reacts.

The change in enthalpy is a measured of the heat evolved of absorbed.

When the heat is released, the change in enthalpy is negative.

The reaction of 2 moles of Na develops 368.4 kj of energy.

Calculate the number of moles of Na in 1.90 g to find the heat released when this quantity reacts.

Atomic mass of Na: 23 g/mol

#mol Na = 1.90 g / 23 g/mol = 0.0826 mol

Do the ratios: [368.4 kj/2mol ] * 0.0826 mol = 15.21 kj.

Then the answer is that 15.21 kj of heat is released (evolved)