What volume of O2 at 1.86 106Pa and 375 K is required to completely react with 1.78 L of H2 at the same temperature and pressure to produce H2O? How many O2 and H2 molecules have reacted?

Answer 1

Write the balanced equation for the reaction taking place:

2H₂ + O₂ ==> 2H₂O

Since the temperature and pressure remain constant, liters and moles become interchangeable. Thus ...

1.78 L H₂ x 1 L O₂ / 2 L H₂ = 0.89 L of O₂ are required

To find the number of molecules of H2 and O2 that have reacted, we will have to find the moles of each first. This will require us to use the temperature and pressure.

PV = nRT

P = pressure in atm = 1.86x10⁶ Pa x 1 kPa/10³ Pa x 1 atm / 101.325 kPa = 18.36 atm

V = volume in L = 0.89 L

n = moles = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in K = 375K

n = PV/RT = (18.36)(0.89) / (0.0821)(375) = 0.531 moles of O₂

Molecules of O₂ = 0.531 moles x 6.022x10²³ molecules / mol = 3.20x10²³ molecules of O₂

Molecules of H₂ = 3.20x10²³ molecules of O₂ x 2 molecules H₂ / molecule O₂ = 6.40x10²³ molecules H₂