Question

Calculate the enthalpy of adsorption of hydrogen gas on platinum at 298 K, given that the maximum coverage of hydrogen on the platinum surface is 0.5 monolayers and the equilibrium constant for the process at 298 K is 2.5 x 10^3. Assume that the adsorption process is exothermic and that the standard enthalpy of formation of water is -286 kJ/mol.

Answer 1

To calculate the enthalpy of adsorption of hydrogen gas on platinum, we can use the van't Hoff equation, which relates the equilibrium constant  K  to the standard enthalpy change  H  and temperature  T :ln K  = -H / R *  1/T  + ln A where R is the gas constant  8.314 J/molK  and A is a constant. In this case, we are given the equilibrium constant  K  at 298 K and we need to find H.Rearranging the equation to solve for H:H = -R * T * ln K  /  1/T Plugging in the given values:H = - 8.314 J/molK  *  298 K  * ln 2.5 x 10^3  /  1/298 K H = -24592.84 J/molSince the adsorption process is exothermic, the enthalpy of adsorption will be negative. To convert the value to kJ/mol, divide by 1000:H = -24.592 kJ/molTherefore, the enthalpy of adsorption of hydrogen gas on platinum at 298 K is approximately -24.6 kJ/mol.