Before moving onto analyzing some examples, here are few reminders.📝
🧐The volume occupied by one mole of a gas is called the molar volume which is 24 dm3 / 24000 cm3
🧐Number of moles of gas = Volume of gas / Molar Volume of gas
* Under the same temperature and pressure ❗️ ❕
Example 1👇
What is the number of moles of methane in 1.44 dm3 of the gas measured at room temperature and pressure?
(Molar Volume of gas at room temperature and pressure= 24 dm3mol-1)
Answer: No of moles of methane= Volume of methane/Molar volume of gas
Therefore, 1.44 dm3 / 24 dm3mol-1 = 0.0600 mol
Yup, keep in mind that for some questions all you need to do is substitute the correct values into the equation.
*Watch out for the units too ❗️ ❕
Example 2👇
What is the volume, measured at room temperature and pressure, occupied by 13.2 g of carbon dioxide?
(Relative atomic masses: C=12, O=16; Molar Volume of gas at room temperature and pressure= 24 dm3mol-1 )
Step 1: Find the moles of CO2
🧐Moles= Mass / Molar Mass
Thus, moles of CO2 = 13.2 g / (12+16+16) = 0.300 mol
💪Final Step: Rearrange the formula to find the volume of gas
🧐 Volume of CO 2 = Moles of CO2 × Molar Volume of Gas
Volume of CO 2= 0.300 mol × 24 dm3mol-1 = 7.20 dm3
Example 3👇
Butane burns in oxygen completely to produce carbon dioxide and water according to the following equation:
2C4H10(g) + 13O2(g) ⇒ 8CO2(g) + 10H2O(l)
What volume of oxygen is needed for the complete combustion of butane measured at room temperature and pressure?
(Molar Volume of gas at room temperature and pressure= 24 dm3mol-1= 24000 cm3 mol-1)
Step 1: Find the moles of C4H10 using the formula
Moles of C4H10= Volume of C4H10/ Molar Volume of gas
Hence, 480 cm3/ 24000 cm3mol-1=0.02 mol
Step 2: Use mole ratio to find the moles of O2
🧐From the equation, 2 moles of C4H10 require 13 moles of O2
Moles of O2 = 0.02 × (13/2) = 0.130 mol
💪Last Step: Rearrange the formula to find the volume of O2
🧐 Volume of O2 = Moles of O2 × molar Volume of gas
Volume of O2 = 0.130 mol × 24 dm3mol-1 = 3.12 dm3
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