Question

If a gas at STP occupies 72.0 L, how many moles of gas are present?

a) 2 moles
b) 3 moles
c) 4 moles
d) 5 moles

Answer 1

At Standard Temperature and Pressure (STP), one mole of an ideal gas occupies 22.4 liters. To find the number of moles in 72.0 liters, divide by the molar volume, which gives approximately 3 moles. Hence, the answer is (b) 3 moles.

Step-by-step explanation:

The student's question asks how many moles of gas are present if a gas at Standard Temperature and Pressure (STP) occupies 72.0 liters. To answer this, we use the concept of molar volume. At STP, one mole of an ideal gas occupies 22.4 liters. Therefore, to find the number of moles in 72.0 liters of gas, we can divide the total volume by the molar volume.

Calculation:
Number of moles = Total Volume / Molar Volume at STP
= 72.0 L / 22.4 L/mol
= 3.214 moles.

Considering standard significant figures and rounding to the nearest whole number, the number of moles present is 3 moles. Therefore, the correct answer is option b) 3 moles.