Question

Consider the reaction.

CH4(g)+2O2(g) -> CO2(g)+2H20(g)

How many grams of methane should be burned in an excess of oxygen at STP to obtain 5.6 L of carbon dioxide?
A. 2.0 g
B. 4.0 g
C. 16.0 g
D. 32.0 g

Answer 1

molar masses

methane = 16 g/mol
carbon dioxide =44 g/mol


One mole of any gas at S.T.P. occupies the same volume which is 22.4 L.

divide this into 5.6 L to find how many grams we have:

5.6/22.4 = 0.25, so there are (0.25)(44 g) = 11 g.

we see that 1 mole of CO2 is produced for 1 mole of CH4

Since we produce 11 g = 0.25 mol of CO2

we must start with 0.25 mol of CH4 (0.25)(16 g) = 4.0 g.