Lesson 21: Moles, Mass & Stoichiometry 🧮🧪💡
Greetings, learners! 🎓🔍 In today's lesson, we're diving deeper into the realm of stoichiometry! You'll learn how to calculate the number of moles of reactants needed to form a certain number of moles of products, and how to determine the mass of a certain number of moles of a substance. This is a powerful tool in the world of chemistry, so buckle up! 🚀⚖️
Prerequisite Material Quiz 📚🧠
What is the relationship between moles, mass, and molar mass?
How can we determine the number of moles of a substance from its mass?
Can we find the mass of a substance if we know the number of moles?
(Answers at the end of the lesson)
Explanation: Moles, Mass & Stoichiometry 🧐👩🔬
In chemistry, the relationship between the mass of a substance, its molar mass, and the number of moles it contains is of paramount importance. Once we know the balanced chemical equation, we can use stoichiometric calculations to determine these quantities and how they relate to each other in a reaction! 🧮🧪
The equation m = n x M is a powerful tool in these calculations, where:
m is the mass of the substance,
n is the number of moles, and
M is the molar mass.
Examples 🌍🔬🔎
Let's consider the reaction 2Fe + 3Cl2 → 2FeCl3.
To balance the equation, we see it's already balanced as it stands.
The ratio of reactants to products by mass is 112g of Fe (2 moles) + 213g of Cl2 (3 moles) = 325g of FeCl3 (2 moles). We verify that mass is conserved in the reaction, as 325g = 325g.
To find the number of moles of a reactant needed to form a certain number of moles of product, we see that to form 4 moles of FeCl3, we need 4 moles of Fe (because the ratio is 1:1).
To find the mass of a product formed from a given mass of reactant, we see that 35.5g of Cl2 (about 0.5 moles) will produce approximately 54.2g of FeCl3. Also, about 18.7g of Fe will be consumed in the process.
Let's Practice More Examples! 👩🔬📚
Example 1: Consider the reaction 2H2 + O2 → 2H2O. If you have 4 moles of H2, how many moles of O2 are needed and how many moles of H2O will be produced?
Answer: 2 moles of O2 are needed and 4 moles of H2O will be produced.
Example 2: For the reaction 4Al + 3O2 → 2Al2O3, if you start with 10.8g of O2 (0.3375 moles), what mass of Al2O3 (Aluminum Oxide) will be produced?
- Answer: In this reaction, 3 moles of O2 yield 2 moles of Al2O3. So, 0.3375 moles of O2 will yield 0.3375 * (2/3) = 0.225 moles of Al2O3. Now, to calculate the mass, we multiply the number of moles by the molar mass of Al2O3, which is approximately 101.96 g/mol. So, the mass of Al2O3 formed is 0.225 moles * 101.96 g/mol ≈ 22.94 g of Al2O3.
3. Example 3: For the reaction N2 + 3H2 → 2NH3, how many grams of NH3 will be produced when you start with 28g of N2?
- Answer: Here, 1 mole of N2 (which is 28g by molar mass) produces 2 moles of NH3. The molar mass of NH3 is approximately 17g/mol. Therefore, the mass of NH3 produced is 2 moles * 17g/mol = 34g of NH3.
Great work everyone! 🎉🔬 Don't forget to practice more problems and ask questions whenever you're in doubt. Remember, practice makes perfect! 👩🔬🧪🌟
Prerequisite Material Quiz Answers 📚🧠
Moles, mass, and molar mass are all interconnected! The number of moles (n) of a substance is the mass (m) divided by the molar mass (M): n = m/M. Conversely, we can determine the mass of a substance if we know its number of moles and molar mass: m = n*M.
To determine the number of moles from the mass of a substance, we simply divide the mass by the molar mass.
Yes, we can determine the mass of a substance if we know the number of moles. We multiply the number of moles by the molar mass of the substance to find the mass.
Keep up the excellent work, chemists! Your journey into the microscopic world of atoms and molecules is just beginning! 💫🔬🌍
Next Lesson: Limiting Reagents and Excess Reagents! Stay tuned! 🎓📚🧪