HELPUL EQUATIONS, CONSTANTS, UNITS

R = gas constant = 0.00831 MPa kg mol^-1 K^-1

M = molal weight of water = 0.018 kg mol^-1

V = molal volume of water = 0.018 liter mol^-1

chemical potential = energy mol^-1

ψ = energy volume^-1 = force area^-1 (pressure)

ψ = ψ_π + ψ_p + ψ_g                                                            

ψ_g = ρ_wgh = 0.01 MPa m^-1. See text p. 44 for definition of terms ρ_w, g and h

MPa = 10 bars = ~10 atmospheres = ~760 mm Hg 9at sea level)

conductance = 1/resistance

van't Hoff equation: ψ_π = - miRT   where
m = molal concentration of the solute (moles solute per 1000 g H₂O)
i = ionization constant of the solute (e.g. 1.8 for NaCl)
R = gas constant
T = absolute temperature (^oK) = 273 + ^oC

Raoult's Law: the lowering of the vapor pressure of a solvent is directly proportional to the number of moles of solute dissolved in it

Flux = (conductivity)(driving force)
with the driving force for water and solutes usually a concentration gradient or pressure gradient

Fick's first law (of diffusion):

See text p. 41 for definition of terms

Poiseuille's equation:

Transpiration:

See web topic 4.4 for definition of terms cwv, rs and rb

Units for transpiration: mg m^-2 s^-1; mmol m^-2 s^-1

Unit for stomatal conductance: mmol m^-2 s^-1; mm s^-1

Unit for net photosynthetic rate (carbon exchange rate, CER: μmol m^-2 s^-1

Summary equation for photosynthesis: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O