第一题：设该烷烃分子式为CnH2n+2.由CH2=CH2+3O2→2CO2+2H2O,即1体积乙烯消耗3体积O2,由题得是等体积混合,所以是0.5体积的乙烯消耗了1.5体积的O2,还剩下4.75-1.5=3.25体积的氧气.CnH2n+2+n+（2n+2）/4O2→nCO2+（2n+2）/2H2O.∴2CnH(2n+2)+(3n+1)O2=2nCO2+2(n+1)H20
2 3n+1
0.5 3.25
解得n=4,所以该烷烃分子式为C4H10 （2）你是否没输入完整?第二题.由PV=nRT.可得,压强比=物质的量比设该气态烷烃分子式为CnH2n+2,CnH2n+2+n+(2n+2)/4O2→nCO2+(2n+2)/2 H2O1.2*[1+n+(2n+2)/4]=n+n+1n=4.所以该烷烃分子式为C4H10