What will be the standard molar volume of He, if its density is \(0.1784 \mathrm{~g} / \mathrm{L}\) at STP? (a) \(11.2 \mathrm{~L}\) (b) \(22.4 \mathrm{~L}\) (c) \(5.6 \mathrm{~L}\) (d) \(2.8 \mathrm{~L}\)

Understanding Standard Temperature and Pressure (STP) is critical for students who are delving into the basics of chemistry and gas laws. STP is a set of conditions for measuring gas volume where the temperature is 0 degrees Celsius (273.15 K) and the pressure is 1 atmosphere (atm). At STP, one mole of any ideal gas occupies 22.4 liters, a crucial point that simplifies calculations and is considered an essential concept for working with gases.

The importance of STP arises from its consistency; it provides a reference that chemists and students can rely upon when comparing the behavior of different gases. Without these standardized conditions, comparisons would be difficult due to the variable nature of gases which are highly sensitive to changes in pressure and temperature.

The molar mass of helium (He) is another fundamental concept students must grasp, especially in the context of gas problems. Helium is an inert noble gas with the atomic number 2, and its molar mass is 4.00 grams per mole (g/mol).

This value is calculated by adding the masses of the individual atoms within one mole of helium, which in this case, since helium is a monatomic gas (consisting of single atoms), is simply the mass of a single helium atom multiplied by Avogadro's number (\(6.022 \times 10^{23}\text{atoms/mol}\)). This molar mass allows us to convert between grams and moles of helium, a key step in solving many chemistry exercises involving gases.

The concept of 'moles of gas' is fundamental to chemical analyses and calculations. A mole is a unit of measure that represents a specific number of particles, usually atoms or molecules. For any substance, one mole is \(6.022 \times 10^{23}\text{particles}\), known as Avogadro's number.

In the context of gases, understanding how to calculate moles is vital. It allows students to establish relationships between various properties such as the volume, temperature, and pressure of a gas. As showcased in the textbook solution, determining the moles of a gas can involve using its density and molar mass. By dividing the density of the gas (grams per liter) by its molar mass (grams per mole), we can find the number of moles of gas within a given volume. This concept is a stepping-stone to mastering more complex topics such as the ideal gas law and determining the behavior of gases under various conditions.