pV = nRT where: p = pressure; V = volume; T = temperature; n = moles; R = molar gas constant. pV/T = constant from multiplication of the 3 gas laws (Boyle's, Charles, Pressure Law). The constant depends on the amount of gas used, which makes sense since more molecules of gas will occupy a greater volume. Hence the nR term accounts for the number of moles of gas. Assumptions (5 from the following): - The gas contains a very large number of particles (meaning a statistical 'average value' for any dynamic variable is truly representative of the gas a whole). - The particles move randomly and rapidly. - Collisions between particles, and particles and the container walls, are perfectly elastic (kinetic energy is not lost). - The particles' motion is dictated by Newton's Laws. - Attractive forces between particles are negligible. - Forces during collisions are instantaneous. - Compared to the volume of the container, the particles have negligible volume.