A0.55 g sample of h20 contains how many
molecules of water?
answer in units of molec.

Explanation:

Num of molecules = num of moles * Avogadro's constant (6.02* 10^23)

But num of moles = reacting mass / molar mass

Molar mass of H20= 2*1 + 16 = 2+16 = 18g

Reacting mass of H20 = 0.55g

Therefore, num of moles of H20 = 0.55g/18g = 0.031 moles

Therefore, num of molecules of H20 = 0.031 * 6.02*10^23

= 1.87*10^22 molecules of H20

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.