Understanding the Mole Concept
In chemistry, the mole is a fundamental unit used to express the amount of a chemical substance. Just as a "dozen" refers to 12 items, a "mole" refers to a specific number of particles (atoms, molecules, or ions). This number is known as Avogadro's Constant ($N_A$).
Avogadro's Constant
Avogadro's constant represents the number of particles in exactly one mole of a substance: $$N_A \approx 6.022 \times 10^{23} \text{ molecules/mole}$$
The Formula
To find the number of molecules ($N$) in a given amount of moles ($n$), we use the following relationship: $$N = n \times N_A$$
Where:
- $N$ is the number of molecules.
- $n$ is the number of moles.
- $N_A$ is Avogadro's constant ($6.022 \times 10^{23}$).
Solving the Problem
Question: How many molecules are contained in 0.35 mole of $N_2$?
Step-by-Step Solution:
Identify the given values:
- Number of moles ($n$) = 0.35 mol
- Avogadro's constant ($N_A$) = $6.022 \times 10^{23} \text{ mol}^{-1}$
Apply the formula: $$N = 0.35 \text{ mol} \times (6.022 \times 10^{23} \text{ molecules/mol})$$
Calculate the result: $$N = 2.1077 \times 10^{23}$$
Rounding to two significant figures (based on the input 0.35), we get: $N \approx 2.1 \times 10^{23}$ molecules of $N_2$.
Why is this important?
Understanding how to convert moles to molecules allows chemists to translate macroscopic quantities (what we can weigh in a lab) into microscopic numbers (the actual number of particles interacting in a reaction). Whether you are dealing with $N_2$ gas or complex compounds, the relationship remains the same!