Changing the pressure of a reaction between hydrogen gas H2 and iodine gas I2 affects the rate of reaction due to the principles of collision theory. The reaction between hydrogen and iodine gases can be represented by the following equation:H2 g + I2 g 2HI g Collision theory states that for a reaction to occur, the reactant particles must collide with each other with sufficient energy and proper orientation. The rate of reaction depends on the frequency and effectiveness of these collisions.When the pressure of the reaction system is increased, the concentration of the reactants H2 and I2 also increases. This is because the gas particles are compressed into a smaller volume, leading to a higher number of particles per unit volume. As a result, the frequency of collisions between H2 and I2 molecules increases, which in turn increases the rate of reaction.However, it is important to note that this reaction is reversible, as indicated by the double arrow in the equation. When the pressure is increased, the system will try to counteract the change and restore equilibrium according to Le Chatelier's principle. In this case, the system will shift towards the side with fewer moles of gas to reduce the pressure. Since there are two moles of gas on the right side 2HI and only one mole of gas on each side of the reactants H2 and I2 , the equilibrium will shift towards the formation of more HI molecules. This shift in equilibrium will also contribute to an increased rate of reaction.In summary, increasing the pressure of a reaction between hydrogen gas and iodine gas will increase the rate of reaction due to the increased frequency of collisions between reactant molecules and the shift in equilibrium towards the formation of more HI molecules, as explained by collision theory and Le Chatelier's principle.