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What mass of water is made when 10 dm^3 of hydrogen gas burns completely in excess air? Please show your work. Thank you. 

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We assume standard conditions.

1 mol of H2 takes .....22.4 liters (dm^3)

x mol of H2 take .......10 liters (dm^3)

x=  10/22.4 =0.446 mol H2

1 mol of H2 has a mass of .........2 grams

0.446 mol of H2 have a mass of... y  grams

y = 0.446*2 =0.893 grams of H2

The balanced chemical reaction of burning hydrogen in oxygen is

2*H2 +O2 = 2*H2O

Molecular masses are

M(H2) = 2 grams

M(H2O) = 2+16 =18 grams

As can be seen from the above equation

2*2 grams of H2 give..... 2*18 grams of H2O

0.893 grams of H2 give.... z grams of H2O

z = 2*18*0.893/(2*2) =8.036 grams of H2O

The mass of the water H2O resulting from burning 10 dm^3 of hydrogen H2 is 8.036 grams.

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