某烃的分子式为CxHy 该烃在氧气中完全燃烧时,n(CxHy):n(O2)=1:5 求x+y=?

反应式为:
CxHy + (x + y/4) O2 == xCO2 + (y/2)H2O
n(CxHy):n(O2)=1:5
即 x + y/4 = 5 (x,y 都是正整数)
y必须是4的倍数.
y = 4时:x + 1 = 5,x = 4,x + y = 4+4 = 8 (C4H4,可以是环丁二烯等)
y = 8时:x + 2 = 5,x = 3,x + y = 3 + 8 = 11 (C3H8,丙烷)