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Vapor pressure is the pressure exerted by the vapor of a substance above its liquid or solid phase when it reaches equilibrium. All liquids have vapor pressures due to the distribution of kinetic energies that enable some molecules to escape the liquid's surface and become gaseous. Solids can also exhibit vapor pressure, but it is generally lower than in liquids as molecules in a solid are less mobile. The vapor pressure of a substance is dependent on temperature and is described by the Clausius-Clapeyron equation: \[ ln(P) = -\frac{\Delta H_{vap}}{R}(\frac{1}{T} - \frac{1}{T_0}) + ln(P_0) \] where P is the vapor pressure, ΔH_vap is the enthalpy of vaporization, T is the temperature, T_0 is the reference temperature, P_0 is the vapor pressure at the reference temperature, and R is the gas constant.