AQA AS Physical Chemistry - The Mole & Gases PDF

AS CHEMISTRY 3.1.2 AMOUNT OF SUBSTANCE THE MOLAR GAS VOLUME 1 mole of ANY gas occupies the same volume, at the same temperature and pressure This makes sense, as all gases are made up of atoms and/or molecules. So, the same nu...

AS CHEMISTRY 3.1.2 AMOUNT OF SUBSTANCE THE MOLAR GAS VOLUME 1 mole of ANY gas occupies the same volume, at the same temperature and pressure This makes sense, as all gases are made up of atoms and/or molecules. So, the same number of atoms / molecules (1 mole) occupy the same volume. Molar gas volume at 298K and 1atm (room temperature & pressure) = 24.0dm3 We can use this to calculate the volume or number of moles of a gas at these temperatures. n = number of moles v V = volume (dm3) n 24.0 298K & 1atm HINTS | TIPS | HACKS Read the question carefully. If it states the specific temperatures & pressure listed above, you should use the molar gas volume in your calculation. If you are given anything other than these, you should use the Ideal Gas Equation! Since 1 mole of ANY gas occupies the same volume in the same conditions, you can use the volumes of gases for stoichiometry! How To Use the Molar Gas Volume Molar Gas Volume Equation Hack AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.1.2 AMOUNT OF SUBSTANCE THE IDEAL GAS EQUATION When you are given temperatures and pressure that are different to those stated for molar gas volume, you need to use the Ideal Gas Equation. This equation links: pressure (p), volume (V), moles (n), temperature (T) & the molar gas constant (R). pV = nRT UNITS ARE ALL IMPORTANT HERE! Pressure Pa (Pascals) Volume m3 (meters cubed) Moles Moles Temperature K (Kelvin) J.K-1.mol-1 R (8.31) (Joules per Kelvin per Mole) COMMON UNIT CONVERSIONS Pressure Volume kPa to Pa: x 1000 cm3 to m3: insert “x10-6” after the number e.g. 24cm3 = 24x10-6 m3 dm3 to m3: insert “x10-3” after the number Temperature e.g. 15dm3 = 15x10-3 m3 oC to K: + 273 AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.1.2 AMOUNT OF SUBSTANCE HINTS | TIPS | HACKS A question will provide 4 of the 5 different piece of data, leaving you to calculate the 5th. You will be required to rearrange the equation to do this! P = nRT V = nRT n = PV T = PV V P RT nR Do the required unit conversions BEFORE inputting the data into the equation. It is known as the “ideal” gas law as it assumes that all gases behave “ideally”. What this means is that we are not taking into account any intermolecular forces of attraction (attractions between the molecules) which could affect the relationships between the values. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 AS CHEMISTRY 3.1.2 AMOUNT OF SUBSTANCE CHANGING CONDITIONS The ideal gas equation shows us that pressure, volume and temperature are all linked (along with number of moles and the molar gas constant). If one condition that a particular gas is in is changed, it will have an impact on the others. e.g. If volume is increased, pressure decreases. If temperature is increased, pressure increases. Of course, the number of moles and the molar gas constant do not change, so we can leave these out of the equation. Original Conditions P1V1 = P2V2 New Conditions T1 T2 UNITS ARE NOT IMPORTANT HERE!! So long as the units of pressure, volume and temperature are consistent, you do not have to convert them like with the Ideal Gas Equation. HINTS | TIPS | HACKS A question will provide 5 of the 6 different piece of data, leaving you to calculate the 6th. You will be required to rearrange the equation to do this! How To Use the Ideal Gas Equation AQA www.chemistrycoach.co.uk © scidekick ltd 2024