Water Potential Calculator

Water potential describes the potential energy of water relative to pure water under reference conditions. It predicts the direction in which water will move: water generally travels from a region with higher water potential toward a region with lower water potential. Plant physiologists, soil scientists, and students use this quantity to understand osmosis, water uptake by roots, cell turgor, wilting, and transport through plant tissues. Pure water at atmospheric pressure is assigned a water potential of zero, while dissolved solutes usually make the value negative. This calculator combines solute potential with pressure potential. Solute potential is calculated with the van't Hoff relationship, solute potential equals negative i times C times R times T. The ionization constant i represents the number of dissolved particles produced by each formula unit. It is approximately 1 for substances such as sucrose that do not dissociate, about 2 for ideal sodium chloride, and may differ from an integer in real solutions. C is molar concentration, R is the gas constant expressed as 0.008314 liter megapascals per mole kelvin, and T is absolute temperature in kelvin. The calculator converts an entered Celsius temperature to kelvin automatically. Pressure potential accounts for physical pressure on water. A turgid living cell normally has positive pressure potential, whereas tension in xylem can be represented by a negative pressure potential. Adding pressure potential to solute potential gives the total water potential for this simplified model. Other components, including gravitational and matric potential, can matter in tall plants, dry soils, or porous materials, but they are not included here. Use consistent units and interpret the result in context. An ideal-solution calculation is most suitable for dilute solutions; concentrated or strongly interacting solutions can depart from ideal behavior. A more negative result indicates a stronger tendency to draw in water when compared with a less negative neighboring compartment. The numerical result is useful for coursework and preliminary estimates, but careful laboratory work should use measured osmotic properties and account for every relevant potential component.