Question about volume of gas ...urgent ar~

Question

(1)
20 cm^3 of ethane (C2H6) was exploded with 95 cm^3 of oxygen . What volume of oxygen was left unreacted? (All volumes were measured at room conditions)
2C2H6(g) + 7O2(g) -> 4CO2(g) + 6H2O(l)

(2)
200 cm^3 of hydrogen was exploded with 200cm^3 of oxygen . What is the final volume if all volumes were measured at (a) 25C and 1 atmosphere (b) 105C and 1 atmosphere.

25C and 105C,,
the C means degree celsius ((temperature))

Answer 1

(1)
2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l)
Volume ratio C2H6 : O2 = 2 : 7 = 20 cm3 : 70 cm3
Hence, O2 is in excess, and C2H6 is completely reacted.
Volume of O2 left = 95 - 70 = 25 cm3

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(2)(a)
2H2(g) + O2(g) → 2H2O(l)
Volume ratio H2 : O2 = 2 : 1 = 200 cm2 : 100 cm3
Hence, O2 is in excess, and H2 is completely reacted.
Volume of O2 left = 200 - 100 = 100 cm3
Volume of H2O formed ≈ 0 cm3 (for it is liquid)
Final volume = 100 + 0 = 100 cm3

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(2)(b)
2H2(g) + O2(g) → 2H2O(g)
Volume ratio H2 : O2 = 2 : 1 = 200 cm2 : 100 cm3
Hence, O2 is in excess, and H2 is completely reacted.
Volume of O2 left = 200 - 100 = 100 cm3
Volume ratio H2 : H2O = 1 : 1
Volume of H2O formed = 200 cm3
Final volume = 100 + 200 = 300 cm3