20 mL of propene is reacted with 70 ml of hydrogen at STP to produce propane, according to the equation. Calculate the volume of H2 gas consumed

CH3CHCH2 + H2 ==> CH3CH2CH3

20 mL propene x (1 mol H2/1 mol propene) = 20 mL H2 consumed. There will be 50 mL H2 left.