Question

20 ml of H2 and 50ml of O2 are mixed and exploded at STP. If water is the only product formed , calculate the number of molecules of water produced?

Answer 1

1 mole of H₂ reacts with 0.5 mole of O₂ to form 1 mole of H₂O.
At STP, the volume is directly proportional to moles.

Since 1 mole of H₂ reacts with 0.5 mole of O₂, 20 ml of H₂ reacts with 10ml of O₂ and form 10ml of H₂O.

volume of 1 mole H₂O = 22.4 l = 22400 ml
number of moles in 10ml H₂O = $\frac{10}{22400}= \frac{1}{2240}\ moles$
number of molecules in 1 mole = $6.022 \times 10^{23}$

number of molecules of water in 10ml = $\frac{1}{2240} \times 6.022 \times 10^{23}=2.688 \times 10^{20}\ molecules$

So 2.688×10²° molecules of water are produced.

Answer 2

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1 mole of H₂ reacts with 0.5 mole of O₂ to form 1 mole of H₂O.

At STP, the volume is directly proportional to moles.

Since 1 mole of H₂ reacts with 0.5 mole of O₂, 20 ml of H₂ reacts with 10ml of O₂ and form 10ml of H₂O.

volume of 1 mole H₂O = 22.4 l = 22400 ml

number of moles in 10ml H₂O = $\frac{10}{22400}= \frac{1}{2240}\ moles$

number of molecules in 1 mole = $6.022 \times 10^{23}$

number of molecules of water in 10ml = $\frac{1}{2240} \times 6.022 \times 10^{23}=2.688 \times 10^{20}\ molecules$

So 2.688×10²° molecules of water are produced.

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