Question #e1092
1 Answer
Answer:
(c)
Explanation:
We can solve this problem by first writing the chemical equation for the reaction:
We know that the temperature and pressure remained unchanged throughout the reaction, so let's let these values be those at STP to make things much easier.
At STP, one mole of an (ideal) gas has a volume of

#"X"# :#10cancel("cm"^3)((1cancel("dm"^3))/(10^3cancel("cm"^3)))((1color(white)(l)"L")/(1cancel("dm"^3))) = 0.010# #"L X"# 
#"original O"_2# :#70cancel("cm"^3)((1cancel("dm"^3))/(10^3cancel("cm"^3)))((1color(white)(l)"L")/(1cancel("dm"^3))) = 0.070# #"L O"_2# 
#"CO"_2# :#30cancel("cm"^3)((1cancel("dm"^3))/(10^3cancel("cm"^3)))((1color(white)(l)"L")/(1cancel("dm"^3))) = 0.030# #"L CO"_2# 
#"final O"_2# :#20cancel("cm"^3)((1cancel("dm"^3))/(10^3cancel("cm"^3)))((1color(white)(l)"L")/(1cancel("dm"^3))) = 0.020# #"L O"_2#
Now, using the fact that

#"X"# :#4.46xx10^4# #"mol"# 
#"original O"_2# :#0.00312# #"mol"# 
#"CO"_2# :#0.00134# #"mol"# 
#"final O"_2# :#8.92xx10^4# #"mol"#
The number of carbon atoms in
There are thus
We now have to find the number of
(The
Let's write what the equation looks like so far:
Similarly to how we found the number of
The coefficient of
According to the law of conservation of mass, the number of atoms of

Left:
#10# #"atoms O"# 
Right:
#7# #"atoms O"#
In order to balance it, we can simply place a
One final step! Again, the law of conservation of mass says the atoms of
And therefore, the hydrocarbon is propane,