How is the decomposing of water a chemical change?

The decomposition of water turns into hydrogen and oxygen with electricity causing a chemical change to happen. 

The number of molecules of O₂ present in the container which consists of N₂, O₂ and Ne is 2.68×10²² molecules

We'll begin by calculating the the mole fraction of O₂. This can be obtained as follow:

Mole fraction of N₂ = 0.55

Mole fraction of Ne = 0.25

Total mole fraction = 1

Mole fraction of O₂ =?

Mole fraction of N₂ + Mole fraction of Ne + Mole fraction of O₂ = 1

0.55 + 0.25 + Mole fraction of O₂ = 1

0.8 + Mole fraction of O₂ = 1

Collect like terms

Mole fraction of O₂ = 1 – 0.8

Mole fraction of O₂ = 0.2Next, we shall determine the total mole of the gases in the container. This can be obtained as follow:

Pressure (P) = 1 atm (at stp)

Temperature (T) = 273 (at stp)

Volume (V) = 5 L

Gas constant (R) = 0.0821 atm.L /Kmol

Number of mole (n) =? PV = nRT

1 × 5 = n × 0.0821 × 273

5 = n × 22.4133

Divide both side by 22.4133

n = 0.223 mole

Thus, the total mole  of the gases in the container is 0.223 mole

Next, we shall determine the number of mole of O₂. This can be obtained as follow:

Mole fraction of O₂ = 0.2

Total mole = 0.223 mole

Mole of O₂ =.?

Mole = Total mole × mole fraction

Mole of O₂ = 0.2 × 0.223

Mole of O₂ = 0.0446 mole Finally, we shall determine the number of molecules of O₂ present in the container.

From Avogadro's hypothesis

1 mole of O₂ = 6.02×10²³ molecules

Therefore,

0.0446 mole of O₂ = 0.0446 × 6.02×10²³

0.0446 mole of O₂ = 2.68×10²² molecules

Thus, the number of molecules of O₂ present in the container is 2.68×10²² molecules

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