Avogadro's Law

V is proportional to n (T,P const) V₁n₂ = V₂n₁

For different gases at the same volume, temperature, and pressure, there are equal moles and equal number of gas molecules present. This is known as Avogadro's Hypothesis.

The volume of a gas is proportional to the number of molecules of gas in the sample. The proportion of reacting gases by volume are the same as the proportion of gas molecules reacting.

If we react 2.5 L of H₂ gas with 2.5 L of Cl₂ gas, each at 1.00 atm pressure and 25.0°C, how many molecules of H₂ and Cl₂ react? The HCl gas collected is at 1.00 atm pressure and 25.0°C.

 Calculate the number of molecules of H₂ gas present before the reaction.

Calculate the number of molecules of Cl₂ gas present before the reaction.