Molar Volume (Edexcel GCSE Chemistry)
Revision Note
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Molar Volume
- At room temperature and pressure, the volume occupied by one mole of any gas was found to be 24 dm3 or 24,000 cm3
- This is known as the molar gas volume at RTP
- RTP stands for “room temperature and pressure” and the conditions are 20 ºC and 1 atmosphere (atm)
- From the molar gas volume the following formula triangle can be derived:
The Molar Volume Formula Triangle
Formula triangle showing the relationship between moles of gas, volume in dm3 and the molar volume
- If the volume is given in cm3 instead of dm3, then divide by 24,000 instead of 24:
Formula triangle showing the relationship between moles of gas, volume in cm3 and the molar volume
Moles into Volume
- Here are some examples of how you can manipulate the relationship to find the volume of gas from a given number of moles
Volume = Moles x Molar Volume
Examples of Converting Moles into Volumes Table
Volume into Moles
- Rearranging the formula allows you to calculate the amount of gas in moles from a given volume at RTP
Moles = Volume ÷ Molar Volume
Examples of Converting Volumes into Moles Table
Reacting Masses into Gas Volumes
- Sometimes in problem-solving we have to convert between the mass of a gas and its volume
- This is a two step problem which requires first converting the mass into moles and then from moles into gas volume
- The following example illustrates this:
Worked example
What is the volume of 154 g of nitrogen gas at RTP?
Answer:
Exam Tip
Make sure you use the correct units as asked by the question when working through reacting gas volume questions.
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