Question

1. calculate the number of molecules in 2.5 mol of a substance.

0.15×10^24 molecules
1.51×10^24 molecules
15.1×10^24 molecules
150.5×10^24 molecules

Explanation:

Step1: Recall Avogadro's number

Avogadro's number $N_A = 6.022\times 10^{23}\text{ molecules/mol}$.

Step2: Calculate number of molecules

We have $n = 2.5\text{ mol}$. The number of molecules $N=n\times N_A$. So $N = 2.5\times6.022\times 10^{23}$.
$N=15.055\times 10^{23}=1.5055\times 10^{24}\approx1.51\times 10^{24}\text{ molecules}$.

Answer:

1.51×10²⁴ molecules