Question

Chemical equation for the reaction between ethane gas and oxygen is given below:
$2C_2{H}_6+7O_2\to 4{CO}_2+6H_{2}O$
(a) How many moles of ethane should react to form $20$ mole ${CO}_2$
(b) How many molecules are present in $67.2L$ ethane at STP?

Answer 1

(a) $2$ moles of $C_2{H}_6\equiv 4$ moles of ${CO}_2$
? $\equiv 20$ moles of ${CO}_2$
By cross multiplication,
Number of moles of $C_2{H}_6=10$
(b) $67.2/22.4=3$ moles
$3\times 6.022\times {10}^{23}=18.066\times {10}^{23}$ molecules.