07-28-2009, 04:49 PM
Combinatorial chemistry is a sophisticated set of techniques used to synthesize, purify, analyze, and screen large numbers of chemical compounds, far faster and cheaper than was previously possible. The direct precursor of combinatorial chemistry was the solid-phase synthesis of polypeptides developed by American biochemist Robert Bruce Merrifield in the 1960s, followed by the advances in laboratory automation since then. Initial development of the field has been led by the pharmaceutical industry in the search for new drugs, but its applications are spreading into other fields of chemistry. Other terms associated with this field are parallel array synthesis and high-throughput chemistry.
Thermochemistry is the study of the heat released or absorbed as a result of chemical reactions. It is a branch of thermodynamics and is utilized by a wide range of scientists and engineers. For example, biochemists use thermochemistry to understand bioenergetics, whereas chemical engineers apply thermochemistry to design manufacturing plants. Chemical reactions involve the conversion of a set of substances collectively referred to as "reactants" to a set of substances collectively referred to as "products." In the following balanced chemical reaction the reactants are gaseous methane, CH4(g), and gaseous molecular oxygen, O2(g), and the products are gaseous carbon dioxide, CO2(g), and liquid water H2O(l):
CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) (1)
Reactions in which a fuel combines with oxygen to produce water and carbon dioxide are called combustion reactions. Because natural gas consists primarily of methane, it is expected that reaction (1) will liberate heat. Reactions that liberate heat are termed exothermic reactions, and reactions that absorb heat aretermed endothermic reactions.
The heat associated with a chemical reaction depends on the pressure and temperature at which the reaction is carried out. All thermochemical data presented here are for reactions carried out under standard conditions, which are a temperature of 298 K (24.85°C) and an applied pressure of one bar. The quantity of heat released in a
reaction depends on the amount of material undergoing reaction. The chemical formulas that appear in a reaction each represent 1 mole (see article on "Mole Concept") of material; for example, the symbol CH4 stands for 1 mole of methane having a mass of 16 grams (0.56 ounces), and the 2 O2(g) tells us that 2 moles of oxygen are required. Thermochemistry also depends on the physical state of the reactants and products. For example, the heat liberated in equation (1) is 890 kilojoules (kJ); if, however, water in the gas phase is formed, H2O(g), the heat
released is only 802 kJ. Reversing a reaction like (l), which liberates heat, yields a reaction wherein heat must be supplied for the reaction to occur. The following reaction absorbs 890 kJ.
CO2(g) + 2 H2O(l) → CH4(g) + 2 O2(g) (2)
Thermochemistry is the study of the heat released or absorbed as a result of chemical reactions. It is a branch of thermodynamics and is utilized by a wide range of scientists and engineers. For example, biochemists use thermochemistry to understand bioenergetics, whereas chemical engineers apply thermochemistry to design manufacturing plants. Chemical reactions involve the conversion of a set of substances collectively referred to as "reactants" to a set of substances collectively referred to as "products." In the following balanced chemical reaction the reactants are gaseous methane, CH4(g), and gaseous molecular oxygen, O2(g), and the products are gaseous carbon dioxide, CO2(g), and liquid water H2O(l):
CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) (1)
Reactions in which a fuel combines with oxygen to produce water and carbon dioxide are called combustion reactions. Because natural gas consists primarily of methane, it is expected that reaction (1) will liberate heat. Reactions that liberate heat are termed exothermic reactions, and reactions that absorb heat aretermed endothermic reactions.
The heat associated with a chemical reaction depends on the pressure and temperature at which the reaction is carried out. All thermochemical data presented here are for reactions carried out under standard conditions, which are a temperature of 298 K (24.85°C) and an applied pressure of one bar. The quantity of heat released in a
reaction depends on the amount of material undergoing reaction. The chemical formulas that appear in a reaction each represent 1 mole (see article on "Mole Concept") of material; for example, the symbol CH4 stands for 1 mole of methane having a mass of 16 grams (0.56 ounces), and the 2 O2(g) tells us that 2 moles of oxygen are required. Thermochemistry also depends on the physical state of the reactants and products. For example, the heat liberated in equation (1) is 890 kilojoules (kJ); if, however, water in the gas phase is formed, H2O(g), the heat
released is only 802 kJ. Reversing a reaction like (l), which liberates heat, yields a reaction wherein heat must be supplied for the reaction to occur. The following reaction absorbs 890 kJ.
CO2(g) + 2 H2O(l) → CH4(g) + 2 O2(g) (2)