A Level Chemistry OCR Practice Exam

What is the molar volume of a gas at room temperature and pressure?

1. 22.4 dm3 mol-1

2. 24.0 dm3 mol-1

3. 32.0 dm3 mol-1

4. 18.0 dm3 mol-1

The correct answer is: 24.0 dm3 mol-1

The molar volume of a gas at room temperature and pressure (RTP) is approximately 24.0 dm³ mol⁻¹. This value is determined under standard conditions, which are typically defined as a temperature of about 20-25 degrees Celsius and a pressure of 1 atmosphere. At these conditions, one mole of any ideal gas occupies this volume. The concept of molar volume is important in chemistry because it provides a means to relate the amount of gas in moles to the volume it occupies, allowing for calculations in stoichiometry and gas laws. This definition is specifically significant in laboratory settings where gas reactions may be taking place under these standard conditions. Other values like 22.4 dm³ mol⁻¹ are relevant for gases at standard temperature and pressure (0 degrees Celsius and 1 atmosphere), not room temperature and pressure. The other provided options, such as 32.0 dm³ mol⁻¹ and 18.0 dm³ mol⁻¹, are not associated with the behavior of gases at RTP. Thus, 24.0 dm³ mol⁻¹ is the accepted standard for the molar volume at room temperature and pressure.