To calculate the standard enthalpy change for the reaction between hydrogen gas and chlorine gas to form hydrogen chloride gas, we will use the bond enthalpy values for H-H, Cl-Cl, and H-Cl bonds. The reaction can be represented as:H2 g + Cl2 g 2HCl g First, we need to break the H-H and Cl-Cl bonds, and then form the H-Cl bonds. The standard enthalpy change for the reaction H can be calculated using the following equation:H = Bond enthalpies of bonds broken - Bond enthalpies of bonds formed Let's assume the bond enthalpy values for H-H, Cl-Cl, and H-Cl bonds are X, Y, and Z kJ/mol, respectively. Then, the standard enthalpy change for the reaction can be calculated as:H = [ 1 X + 1 Y ] - [ 2 Z ]Now, we need the bond enthalpy values for H-H, Cl-Cl, and H-Cl bonds. The average bond enthalpy values are:H-H bond: 436 kJ/molCl-Cl bond: 243 kJ/molH-Cl bond: 431 kJ/molNow, we can plug these values into the equation:H = [ 1 436 + 1 243 ] - [ 2 431 ]H = 436 + 243 - 862 H = 679 - 862H = -183 kJ/molThe standard enthalpy change for the reaction between hydrogen gas and chlorine gas to form hydrogen chloride gas is -183 kJ/mol. This means the reaction is exothermic, as energy is released in the form of heat.