Equations of state (EoSs) show how the thermodynamic variables of temperature, pressure and volume are inter-related. The ideal gas law, PV = nRT, is an example of an EoS which is used as a simple but effective model to explain the properties of gases. EoSs can also be applied to solids, where they can be used to show how energy changes when the solid experiences dramatic changes in its environment, which occur for example on the surfaces of planets and their moons. In this beamtime we will derive the EoS of naphthalene, a simple model for the polyaromatic hydrocarbons which are thought to be the repository for most of the carbon in the Universe. The results will be used to reveal the changes in different contributions to the thermodynamic properties of naphthalene which occur in response to compression, showing quantitatively how the intermolecular interactions ‘absorb’ pressure.