Question

Vhen 2.0 moles of magnesium reacts, how many liters of oxygen gas, O2, are needed at STP conditions?

- Mg (3) + O2(g) → 2 Mgo (3)

Answer 1

22.4 litres

Explanation:

Reaction:

2Mg (s) + O2 (g) → 2 MgO (s)

From the reaction, we know that 2 moles of Mg (s) react with 1 mol of O2

STP conditions mean:

• absolute temperature of 273.15 K

• absolute pressure of 1 atm

Using the equation of state for ideal gases:

PV = nRT

where P is the absolute pressure, T is the absolute temperature, n are the moles, V is the volume, and R is the gas constant = 0.082 atm*L/(mol*K). Solving for V and replacing:

V = nRT/P

V = 1*0.082*273.15/1

V = 22.4 litres