Increasing the pressure on the gas phase reaction between hydrogen gas H2 and iodine gas I2 to form hydrogen iodide 2HI will generally increase the reaction rate. This effect can be explained using collision theory and the ideal gas law.Collision theory states that for a reaction to occur, the reactant particles must collide with each other with sufficient energy and proper orientation. The reaction rate depends on the frequency of these effective collisions. When the pressure of a gas is increased, the concentration of the gas molecules also increases, as described by the ideal gas law PV=nRT, where P is pressure, V is volume, n is the number of moles, R is the gas constant, and T is temperature . In the case of the H2 + I2 2HI reaction, increasing the pressure leads to a higher concentration of both hydrogen and iodine gas molecules in the reaction vessel. This results in a higher frequency of collisions between H2 and I2 molecules, which in turn increases the probability of effective collisions that lead to the formation of hydrogen iodide. Consequently, the reaction rate increases with increasing pressure.It is important to note that this explanation assumes that the reaction is not at equilibrium and that the increase in pressure does not significantly affect the activation energy or the reaction mechanism.