How Many Molecules Are In 25 Grams Of Nh3

How Many Molecules are in 25 Grams of NH₃? A Deep Dive into Molecular Calculations

Determining the number of molecules in a given mass of a substance is a fundamental concept in chemistry. This article will guide you through the step-by-step process of calculating the number of molecules in 25 grams of ammonia (NH₃), explaining the underlying principles and relevant concepts. We'll cover everything from molar mass calculations to Avogadro's number and offer a detailed explanation suitable for students and anyone interested in learning more about stoichiometry.

Understanding the Fundamentals: Moles and Avogadro's Number

Before we dive into the calculation, let's refresh our understanding of some key concepts. The mole (mol) is the International System of Units (SI) base unit for the amount of substance. One mole of any substance contains Avogadro's number of particles, which is approximately 6.022 x 10²³. These particles can be atoms, molecules, ions, or other specified entities.

Avogadro's number is a crucial constant in chemistry, bridging the microscopic world of atoms and molecules with the macroscopic world of grams and moles. It allows us to convert between the number of particles and the mass of a substance.

Calculating the Molar Mass of Ammonia (NH₃)

The first step in our calculation is to determine the molar mass of ammonia (NH₃). The molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). To calculate it, we need the atomic masses of nitrogen (N) and hydrogen (H) from the periodic table.

• Atomic mass of Nitrogen (N): approximately 14.01 g/mol
• Atomic mass of Hydrogen (H): approximately 1.01 g/mol

Since ammonia (NH₃) has one nitrogen atom and three hydrogen atoms, its molar mass is:

14.01 g/mol (N) + 3 * 1.01 g/mol (H) = 17.04 g/mol

Therefore, the molar mass of NH₃ is approximately 17.04 g/mol. This means that one mole of ammonia weighs 17.04 grams.

Converting Grams to Moles

Now that we know the molar mass of NH₃, we can convert the given mass of 25 grams into moles. We use the following formula:

Moles = Mass (g) / Molar Mass (g/mol)

Plugging in the values:

Moles = 25 g / 17.04 g/mol ≈ 1.47 mol

So, 25 grams of ammonia contains approximately 1.47 moles of NH₃ molecules.

Calculating the Number of Molecules

Finally, we can use Avogadro's number to calculate the number of molecules in 1.47 moles of NH₃. The formula is:

Number of Molecules = Moles × Avogadro's Number

Number of Molecules = 1.47 mol × 6.022 x 10²³ molecules/mol ≈ 8.85 x 10²³ molecules

Therefore, there are approximately 8.85 x 10²³ molecules in 25 grams of ammonia (NH₃).

A Step-by-Step Summary of the Calculation

To reiterate the process, here's a concise summary:

1. Determine the molar mass of NH₃: 14.01 g/mol (N) + 3 * 1.01 g/mol (H) = 17.04 g/mol
2. Convert grams to moles: 25 g / 17.04 g/mol ≈ 1.47 mol
3. Calculate the number of molecules: 1.47 mol × 6.022 x 10²³ molecules/mol ≈ 8.85 x 10²³ molecules

Understanding Significant Figures and Precision

It's important to consider significant figures in our calculations. The given mass of 25 grams has two significant figures. Therefore, our final answer should also have two significant figures. Rounding our result, we get 8.9 x 10²³ molecules. This reflects the precision of our initial measurement.

Further Applications and Considerations

This fundamental calculation forms the basis for many other stoichiometric problems in chemistry. Understanding how to convert between mass, moles, and the number of molecules is crucial for solving problems involving chemical reactions, concentrations, and limiting reactants.

For instance, if we were dealing with a chemical reaction involving NH₃, we could use this calculation to determine the amount of other reactants or products involved based on the stoichiometric ratios in the balanced chemical equation.

Frequently Asked Questions (FAQ)

• Q: What if the given mass was in a different unit, like kilograms?

  A: You would first need to convert the mass to grams before proceeding with the calculation. Remember, the molar mass is expressed in grams per mole.

• Q: Is Avogadro's number an exact number?

  A: While Avogadro's number is often rounded to 6.022 x 10²³, it's actually an experimentally determined value with a degree of uncertainty. However, for most calculations, this level of precision is sufficient.

• Q: Can this calculation be applied to other compounds?

  A: Absolutely! The same steps can be applied to calculate the number of molecules in a given mass of any compound. You would simply need to determine the molar mass of that specific compound using the atomic masses of its constituent elements.

• Q: What if I need to find the number of atoms instead of molecules?

  A: Once you have the number of molecules, you can calculate the number of atoms by considering the number of atoms per molecule. For instance, in NH₃, there are four atoms (one nitrogen and three hydrogen) per molecule. Therefore, you would multiply the number of molecules by four to get the total number of atoms.

Conclusion

Calculating the number of molecules in a given mass of a substance is a cornerstone of chemistry. By understanding molar mass, Avogadro's number, and the conversion process between grams and moles, we can accurately determine the number of molecules present. In this case, we found that 25 grams of ammonia (NH₃) contains approximately 8.9 x 10²³ molecules. This fundamental understanding opens doors to solving more complex stoichiometric problems and exploring the fascinating world of chemical quantities. This method is applicable to a wide range of compounds, solidifying its importance as a core concept in chemistry. Remember to always pay attention to significant figures for accurate and meaningful results.