The reaction between hydrogen gas H2 and iodine vapor I2 to form hydrogen iodide HI can be represented by the following balanced equation:H2 g + I2 g 2HI g This reaction is governed by the principles of chemical kinetics and the rate law. The rate law for this reaction can be expressed as:Rate = k[H2]^x[I2]^ywhere Rate is the reaction rate, k is the rate constant, [H2] and [I2] are the concentrations of hydrogen and iodine, respectively, and x and y are the reaction orders with respect to hydrogen and iodine, respectively.The reaction between hydrogen and iodine is a second-order reaction, meaning that the reaction rate is directly proportional to the square of the concentration of the reactants. In this case, x = 1 and y = 1, so the rate law becomes:Rate = k[H2][I2]Now, let's consider the effect of pressure on the reaction rate. According to the ideal gas law, the concentration of a gas is directly proportional to its pressure at constant temperature:[P] = n/V = n/RT * Pwhere [P] is the concentration of the gas, n is the number of moles, V is the volume, R is the ideal gas constant, and T is the temperature.As the pressure of the system increases from 0.5 atm to 2.0 atm, the concentrations of both hydrogen and iodine will increase proportionally. Since the reaction rate is directly proportional to the product of the concentrations of the reactants, the rate of the reaction will increase as the pressure increases.In conclusion, the rate of the reaction between hydrogen gas and iodine vapor will increase as the pressure is varied over a range of 0.5 atm to 2.0 atm, at a constant temperature.