The enthalpy of adsorption for H2 adsorbed on a surface of copper is -54.4 kJ ·mpl^-1 . The act

step 1 The day by temperature of copper is 345 Kelvin estimate its smaller heat capacity at 100 Kelvin.

The enthalpy of adsorption for H2 adsorbed on a surface of...

The enthalpy of adsorption for $\mathrm{H}_{2}$ adsorbed on a surface of copper is $-54.4 \mathrm{~kJ} \cdot \mathrm{mpl}^{-1} .$ The activation energy for going from the physisorbed state to the chemisorbed state is $29.3 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}$, and the curve crossing between these two potentials occurs at $V(z)=$ $21 \mathrm{~kJ} \cdot \mathrm{mol}^{-1}$. Draw a schematic representation similar to that in Figure $29.20$ for the case of $\mathrm{H}_{2}$ interacting with copper.

Key Concepts

Potential Energy Surface

A potential energy surface (PES) is a multidimensional surface representing the energy of a system as a function of the positions of all its atoms. In adsorption studies, the PES is used to illustrate the energy changes as the adsorbate approaches and interacts with the surface. It helps visualize the energy minima corresponding to physisorbed and chemisorbed states and the transition state between them.

Activation Energy

Activation energy is the energy barrier that must be overcome for a process to occur. In the context of adsorption, it represents the energy required for the adsorbate to transition from the physisorbed state to the chemisorbed state. This barrier is depicted as a hump between the two potential wells in energy diagrams, indicating the need to overcome this threshold to achieve chemisorption.

Enthalpy of Adsorption

The enthalpy of adsorption is the heat change associated with the adsorption process, reflecting the strength of the interactions between the adsorbate and the surface. A negative value indicates that the process is exothermic, releasing heat upon adsorption. This parameter is crucial for understanding the stability and favorability of the adsorbed state in both physisorption and chemisorption.

Curve Crossing

Curve crossing refers to the point where two potential energy curves, often representing different states (such as physisorption and chemisorption), intersect. In adsorption diagrams, the crossing point is critical as it marks the condition where the energies of the two states become equal, influencing the kinetics and mechanism by which the adsorbate transitions from one state to another.

Physisorption

Physisorption is a type of adsorption where the binding forces are primarily weak van der Waals interactions. It generally involves minimal changes to the electronic states of the adsorbate, occurs at lower energies, and is typically reversible. This process is usually represented in energy diagrams by a shallow potential well indicating a relatively weak binding energy.

Adsorption

Adsorption is the process by which particles (atoms, molecules, or ions) adhere to a surface. This phenomenon is fundamental to surface chemistry and plays a significant role in catalysis and sensor technologies. It involves interactions between the adsorbate (the species being adsorbed) and the adsorbent (the material on which adsorption occurs), which can vary in strength and nature.

Chemisorption

Chemisorption involves the formation of a chemical bond between the adsorbate and the surface. This results in a stronger and often irreversible adsorption, characterized by a deeper potential energy well in energy diagrams. Chemisorption usually entails a significant change in the electronic structure of the adsorbate due to the establishment of chemical bonds.

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