The solubility of gases is not constant in all conditions. If temperatures differ, the solubility of gases differ. Additionally, the solvent (the substance that is mixed with a gas to form a solution) can affect the solubility of a gas (its ability to become dissolved and in turn contribute to a formed amount of concentration).
The Effects on the Solubility of Gases in the Universal Solvent
The solubility of a gas is dependent on temperature. An increase in temperature results in a decrease in gas solubility in water, while a decrease in temperature results in an increase of gas solubility in water. To comprehend this phenomena one must consider the two processes that occur when a non-polar gas is added to water. Initially a type of cavity develops when adding the solute to the solvent, representative of the conformation and overall size of the added gas, and in turn a successive process occurs in which attractive forces between the gas and water molecules are stimulated. It is this dual process that induces the water to produce both attractive and repulsive forces. By examining the water on a microscopic level and the components of the water that portray propinquity to the non-polar gases, temperature dependencies become observable.
The Survival of Fish
The solubility of gases in water is influential in the survival of ectotherms, such as fish. Because an increase in temperature contributes to a decline in the solubility of gases in water, warmer water holds less oxygen. Many fish are only capable of living in cooler waters containing more oxygen.
Barotrauma, commonly referred to as "the bends," is tissue damage resulting from effects collocating with pressure, and thus wisth the solubility of gases. This is because pressure and gas solubility are directly proportional according to Henry's Law, C=kP. Scuba divers are made highly susceptible to the bends by subjecting their physiological pressure levels to the dramatically varying pressure levels of the ocean's waters. The high underwater pressure causes the solubility of the gases breathed from a diver's oxygen tank to increase; if a diver rises to the surface of the ocean too rapidly, where the pressure of the atmosphere is less than the pressure within the water, and the solubility of the gases in the atmosphere is decreased, severe injury can affect a diver as a result of gases rapidly leaving the bloodstream.
Making Connections: The Phenomena of Gas Solubility
The reason for the relationship between temperature and gas solubility is similar to that of the relationship between temperature and vapor pressure. An increase in temperature causes an increase in kinetic energy, resulting in a more rapid motion of molecules, breaking intermolecular bonds which enable molecules to escape from the solution. This behavior is described by the Second Law of Thermodynamics.
Scientific Evidence of the Effect of Temperature On Gas Solubility
A study of the effects of temperature control on the formation of soluble fermentation substances from sludge found that VFA generation through fermentation increased by a factor of five with a temperature change of 10-24 degrees Celsius (Cokgor,EU. Oktay,S. 2009).
Solubility: Link to Life
The solubility of gases also influences human life directly. At the University of Lund in Sweden, experimentation with infant formula led to the discovery that performing heat treatment on commercial formula affected the solubility and digestibility of the milk proteins (Boehm, G, Rhaiha, NC. 1994).
The Solubility of Gases in Organic Solvents
Gases assimilated with organic solvents become more soluble at higher temperatures. Le Chatelier's principle can be applied to this behavior. The principle states that when a system is placed under stress, an equilibrium shift will occur in the direction that will relieve the stress. Adding heat to a solution will induce a shift in the equilibrium that favors dissolution in order to reduce heat. On a molecular level, because organic solvents (in contrast to water) are incapable of forming hydrogen bonds with gases, more heat is released when a gas is placed in water than in an organic solvent. Entropy, as well as stronger attractions between a solvent and solute, contribute to an greater transfer of heat, or enthalpy. Thus, increasing the temperature of the solution will favor an endothermic shift in the equilibrium of the system. As a result, the solubility of gases increases with increasing temperature in organic solvents.
The Exception to Gas Solubility
Noble gases, however, have a much more complex solubility. The solubility decreases with increased temperature, eventually reaching a minimum; then the solubility reverses directions, becoming more soluble at higher temperatures.
|Temperature & Water Solubility in Grams of Solute per 100 ml of |
|Temperature(Celsius)||Solid Citric Acid||Solid Potassium Phosphate||Gaseous Nitrogen||Gaseous Oxygen|
(x = not available)
1. Consider two beakers: each contains approximately 30 mL of water. It must be determined which beaker contains the water with the higher solubility of oxygen. What information is needed to make such a determination?
2. A system of cyclopentane and oxygen gas are at equilibrium with an enthalpy of -1234 kJ; predict whether the solubility of oxygen gas will be greater when heat is added to the system or when a temperature decrease occurs.
3. Which family—or group of elements—of the periodic table displays complex solubility behavior? Clicking on the hyperlink under the section The Exception to Gas Solubility, determine which noble gas displays the greatest solubility at 50. C.
4. You purchase a rare species of plant that acquires oxygen through the solution it is placed in. Knowing that the plant will be kept outside over the scorching summer, what type of solution should the plant be placed in to assure that it receives the greatest amount of oxygen possible?
5. Determine the solubility of N2(g) when combined with H2O at .0345 atm. At 0 .C the pressure of N2 is 1.00 atm, and its solubility is 21.0 ml at STP.
1. The temperature of the solution of H2O within the beaker is required.
2. Cyclopentane is an organic solvent. Oxygen gas and cyclopentane in a system at equilibrium, where the entropy is negative, will be be displaced from equilibrium when any type of temperature change is inflicted on the system. Because the dissolution of the gas is endothermic, more heat increases the solubility of the gas.
3. Noble gases; Helium (with a solubility of 1).
4. The plant should be placed in a solution that consists of an organic solvent to assure that, with the increase of the outside temperature, the solubility of oxygen in the solution will also increase.
5. 3.29×10-5M N2
Begin by determining the molarity ( solubility) of N2(g) at O . C and STP.
NOTE: Molarity is equivalent to: mols of solute/ L of solution
At STP 1mol=22L
Molarity of N2 = 21ml ×( 1L/ 1000ml)=.021L N2
=.021L N2×(1mol/22L)=.000954mols/ 1L
= 9.5×10-4 M N2
Now that the molarity of N20. C has been attained, the Henry's law constant, k, can be evaluated.
Henry's Law : C = k Pgas, where C is solubility, k is the constant, and P is the partial pressure of the gas being considered.
Rearranging the formula to solve for k : k=C/Pgas
k= 9.5×10-4 M N2/ 1atm
Now substitute k and the partial pressure of N2 into Henry's law:
C= (9.5×10-4M N2)×(.0345)= 3.29×10-5 M N2
- Petrucci, et al. General Chemistry Principles & Modern Applications. 9th ed. Upper Saddle River, NJ: Pearson Prentice Hall, 2007
- Cokgor, EU, Oktay,S, Tas,Do, Zengin,GE, and Orhon,D. "Influence of pH and temperature on soluble substrate generation with primary sludge fermentation." Environmental Engineering Department.2009.
- Boehm, G, Raiha, NC. "Heat treatment of infant formula: effect on postprandial serum alpha-amino-nitrogen concentrations in very-low-birth-weight infants." Department of Pediatrics. 1994.
- Garde,Shekhar, Garcia, Angel, Pratt, Lawrence, Hummer, Gerhard. "Temperature Dependence of the Non-polar Solubility of Gases in Water". Biophysical Chemistry. Volume 78. Issues 1-2. 1999.
- Becker,G.D., Parell, Joseph. "Barotrauma of the Ears and Sinuses After Scuba Diving." Otology. 2001.
- Michelle Hoang (UCD), Cynthia Dvorsky (UCD)