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# The ideal gas equation

Physical

AS

Amount of Substance

AQA Content

###### Use the equation in calculations.

###### Students will not be expected to recall the value of the gas constant, R.

Specification Notes

###### The ideal gas equation pV = nRT with the variables in SI units.

Notes

###### Learn to use and manipulate the following equation:

###### There's a couple of things to bear in mind when using this equation:

###### Pressure is in pascals* ***not** kilopascals.

###### Volume is in cubic metres, 1 cubic metre = 1 000 000 cubic centimetres

###### Temperature is in kelvin, 0Â°C = 273 K

###### n = number of moles

###### R is the Gas Constant

###### The ideal gas equation relates to a hypothetical ideal gas. To use the equation for real gases, we have to make some assumptions, including:

###### Gases are considered to be made up of sold spheres that move in straight lines. Their direction is random and they are constantly moving.

###### After collisions, kinetic energy is the same as before the collision.

###### Temperature is directly proportional to the kinetic energy of the particles.

###### Molar gas volume

###### At 25Â°C (298 K), atmospheric pressure (p = 101 325 Pa) and using a gas constant, R = 8.31 J Kâˆ’1 molâˆ’1, the volume of 1 mole (n = 1) of a gas is calculated as:

###### pV = nRT

###### V = nRT/p = (1 Ã— 8.31 Ã— 298)/101325 = 0.0244m3

###### V = 24.4 dm3

###### 24 dm3 is used as the molar gas volume for 1 mole of any gas at 25Â°C and atmospheric pressure.

##### Examples

##### 1.

##### 2.

##### Exam Question

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