In the combustion of hydrogen gas, hydrogen reacts with oxygen from the air to form water vapor.
hydrogen+oxygen-> water
if you burn 39.7 g of hydrogen and produce 355g of water, how much oxygen reacted?

The reaction equation:
2H₂ + O₂ → 2H₂O
Moles = mass/molecular mass
The moles of Hydrogen present:
39.7/2 = 19.85 moles
The moles of water present:
355/18 = 19.72
The moles of water that should have been formed according to equation:
moles Hydrogen = Moles water = 19.85
Because less than the predicted amount of water is formed, we know that Hydrogen is in excess and Oxygen is the limiting reactant. We will calculate the moles of Oxygen using moles of water.
Molar ratio of Oxygen : Water = 1:2
Moles of Oxygen = 19.72/2 = 9.86
Mass of Oxygen = 315.52 grams

Answer : option c) heat is released during the process.explanation :

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.

Idon't know hope someone you