Use PV =nRT. Rearrange it to n = PV/RT.
P = 202.6 kPa
V = 4.0L
R = 8.314 kPa*L/mol*K
T = 127 °C + 273 = 400 K
Plug it in and solve. I got 0.24 moles of H2.
Answer : The number of moles of water will be, 1.235 moles
Solution : Given,
Mass of
= 42 grams
Molar mass of
= 34 g/mole
First we have to calculate the moles of 

Now we have to calculate the moles of water.
The balanced chemical reaction will be,

From the balanced reaction, we conclude that
As, 2 moles of
decomposes to give 2 moles of water
So, 1.235 moles of
decomposes to give 1.235 moles of water
Therefore, the number of moles of water will be, 1.235 moles
Both derive from H20, one is agitated molecules from being heated up. The other molecules are slowed down by being cooled.
A (they are experimentally determined exponents)