1) If 6.25 moles of CO2 are produced, how many moles of O2 were used?

1 mol of methane is 16 grams. Therefore, if you have 100 grams of methane, it means that you have

100

16

=

6.25

moles of methane.

When you burn 6.25 moles of methane, you produce 6.25 moles of carbondioxide.

Your reaction is wrong though. I want to correct it.

C

H

4

+

2

O

2

→

C

O

2

+

2

H

2

O

When you burn 6.25 moles of methane, you need 12.5 moles of oxygen gas.

When you burn 6.25 moles of methane, you produce 6.25 moles of carbondioxide (275 grams of

C

O

2

) and 12.5 moles of water vapour (225 grams of

H

2

O

).