Question

Consider the following chemical reaction: 2H2O(l)→2H2(g)+O2(g)

What mass of H2O is required to form 1.6 L of O2 at a temperature of 305 K and a pressure of 0.951 atm ?

m=?? g

Answer 1

For the decomposition reaction of water as given, you have to determine, 1.6 L of oxygen produces how much amount of water at 305 K temperature and 0.951 atm pressure. For this first of all you will have to know the moles of oxygen used by converting liters of oyxgen to moles using Ideal gas equation:

PV=nRT

[Since all the values are in standard units, no unit conversion is required)

(0.951atm) (1.6L) = n (0.0821) (305K)

n = (0.951atm) (1.6L) / (0.0821) (305K)

n = 0.0607 moles

Now the moles of water consumed per reaction can be calculated using the stochiometry of the reaction as:

1 mole oxygen produced by 2 moles of water. Thus

number of moles of water used will be

n = n oxygen X 2

n = 0.0607 X 2

n = 0.1215 moles

To finally get the mass of water from number of moles, simply multiply the number of moles of water by

molecular mass of water i.e. 18

m = n X MM

m = 0.1215 X 18

m = 2.187 g