chemistry combustion help

hi! i’ve tried these two questions and can’t seem to understand them at all because the algebra throws me in for a loop. could someone explain how to work these out?

1) Alkenes have a general formula CnH2n
When alkenes undergo combustion,

CnH2n+2 + xO2 -> nCO2 + (n+1)H2o

determine x in terms of n

thank you!

Reply 1

TypicalNerd

Original post by meowsies

You would expect the total numbers of oxygen atoms on both sides to be the same, because otherwise the equation would be unbalanced and it wouldn’t obey the law of conservation of mass.

On the LHS, because you have xO2, there are 2x atoms of oxygen (2 times the x in front of the O2).

On the RHS, there is nCO2 and (n + 1)O2. Can you use this to:

(a) work out how many oxygen atoms there are in n O2 molecules?

(b) work out how many oxygen atoms there are in (n+1) H2O molecules?

(c) add up these expressions to find how many oxygen atoms there are in total on the RHS?

(d) set your answer to (c) equal to the 2x and then halve both sides to get x?