What does the Kelvin equation tell us about?

The Kelvin equation describes the change in vapour pressure due to a curved liquid–vapor interface, such as the surface of a droplet. The vapor pressure at a convex curved surface is higher than that at a flat surface.

What is the term Po in the Kelvin equation?

d) PO is the elevated vapour pressure. Explanation: The Kelvin equation for the lowering in vapour pressure due to capillaries is given as-

What is capillary condensation in bet?

Capillary condensation is the “process by which multilayer adsorption from the vapor [phase] into a porous medium proceeds to the point at which pore spaces become filled with condensed liquid from the vapor [phase].” The unique aspect of capillary condensation is that vapor condensation occurs below the saturation …

How do you find the vapor pressure of a droplet?

Vapor Pressure of a Liquid at Curved Liquid Air Interface Kelvin’s equation ln(PPs)=2γVmrRT ⁡ ( P P s ) = 2 γ V m r R T relates the saturation vapor pressure Ps of a liquid at some given temperature T to the vapor pressure P above a curved liquid surface of radaus r. The term R stands for the gas constant.

What causes surface tension?

The surface tension arises due to cohesive interactions between the molecules in the liquid. At the bulk of the liquid, the molecules have neighboring molecules on each side. Molecules are pulling each other equally in all directions causing a net force of zero.

What is hysteresis loop adsorption?

In materials containing a portion of mesopores, a hysteresis loop is frequently observed , i.e. where the adsorbent loading and regeneration follow different paths in the adsorbed phase concentration versus partial pressure space. An example of such a hysteresis loop is illustrated in Figure 1.

How do you calculate pore volume from a bet?

To know the meso/macropore volume, the isotherm must reach a plateau at which point a total volume approximation can be calculated (so-called Gurvich volume). Then if you really want to stretch the math, you can employ the relationship between area and volume of a cylinder to calculate a pore size (d = 4V/A).

What is the formula for calculating vapor pressure?

To find the vapor pressure at a given temperature, use the Clausius-Clapeyron equation: ln(P1/P2) = (ΔHvap/R)((1/T2) – (1/T1)). You could also use Raoult’s Law to find the vapor pressure: Psolution=PsolventXsolvent.

Why meniscus is formed?

Water molecules are attracted to the molecules in the wall of the glass beaker. And since water molecules like to stick together, when the molecules touching the glass cling to it, other water molecules cling to the molecules touching the glass, forming the meniscus.

Why is water polar?

The unequal sharing of electrons between the atoms and the unsymmetrical shape of the molecule means that a water molecule has two poles – a positive charge on the hydrogen pole (side) and a negative charge on the oxygen pole (side). We say that the water molecule is electrically polar.

What is Type 2 adsorption isotherm?

The reversible Type II isotherm is the normal form of isotherm obtained with a non-porous or macroporous adsorbent. The Type II isotherm represents unrestricted monolayer-multilayer adsorption.

What is sorption and desorption isotherm?

Abstract. Sorption isotherms describe the relation between the equilibrium moisture content of a material and the ambient relative humidity. Most materials exhibits sorption hysteresis, that is, desorption give higher equilibrium moisture contents than absorption at equal ambient climate conditions.

How do you calculate pore distribution?

The pore-size distribution (PSD) can be defined as either p(r)=dV/dr or p(r)=(1/Vp)dV/dr, where Vp is the total pore volume.

How is surface area determined by BET isotherm method?

BET surface areas were determined from the calculated isotherms by the same method used for treating experimental data. The BET analysis is performed by plotting x/v(1 − x) vs x, where x = P/P0 (P0 = 1 bar) and v is the volume of nitrogen adsorbed per gram of MOF at STP.

How do you find heat of vaporization given temperature and pressure?

If the problem provides the two pressure and two temperature values, use the equation ln(P1/P2)=(Hvap/R)(T1-T2/T1xT2), where P1 and P2 are the pressure values; Hvap is the molar heat of vaporization; R is the gas constant; and T1 and T2 are the temperature values.

How do you calculate meniscus?

Measure so that the line you are reading is even with the center of the meniscus. For water and most liquids, this is the bottom of the meniscus. For mercury, take the measurement from the top of the meniscus. In either case, you are measuring based on the center of the meniscus.