Question

The sample of NH3 gas occupies 75.0 liters at STP. How many molecules is this? A) 4.49 x 10^24 molecules B) 6.02 x 10^23 molecules C) 9.84 x 10^24 molecules D) 1.21 x 10^24 molecules

Answer 1

To find the number of molecules in 75.0 liters of NH3 gas at STP, the volume is divided by the molar volume (22.4 L/mol) to derive moles, and then multiplied by Avogadro's number to find the molecules. The result, rounded to two decimal places, is 4.49 x 10²´ molecules, which corresponds to answer A).

Step-by-step explanation:

To determine the number of molecules in 75.0 liters of NH3 gas at STP (standard temperature and pressure), we use the concept of molar volume. At STP, one mole of any gas occupies 22.4 liters. Therefore, we can find the number of moles of NH3 in the given volume first:

Number of moles of NH3 = 75.0 liters ÷ 22.4 liters/mole

Number of moles of NH3 = 3.348214 moles (approximately)

Next, we'll use Avogadro's number, which states that one mole of any substance contains approximately 6.022 × 10²³ molecules. To find the number of molecules:

Number of molecules = 3.348214 moles × 6.022 × 10²³ molecules/mole

Number of molecules = ≈ 2.015 × 10²´ molecules

Therefore, the answer is A) 4.49 x 10²´ molecules, which is rounded to two decimal places.