Search results
Results From The WOW.Com Content Network
An energy profile of an exothermic reaction. In an exothermic reaction, by definition, the enthalpy change has a negative value: ΔH = H products - H reactants < 0. where a larger value (the higher energy of the reactants) is subtracted from a smaller value (the lower energy of the products). For example, when hydrogen burns: 2H 2 (g) + O 2 (g ...
An exothermic thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake. Some examples of exothermic processes are: [14] Combustion of fuels such as wood, coal and oil/petroleum; The thermite reaction [15] The reaction of alkali metals and other highly electropositive metals ...
Typical examples of exothermic reactions are combustion, precipitation and crystallization, in which ordered solids are formed from disordered gaseous or liquid phases. In contrast, in endothermic reactions, heat is consumed from the environment. This can occur by increasing the entropy of the system, often through the formation of gaseous or ...
A classical example is the decomposition of mercuric oxide to give oxygen and mercury metal. The reaction was used by Joseph Priestley to prepare samples of gaseous oxygen for the first time. When water is heated to well over 2,000 °C (2,270 K; 3,630 °F), a small percentage of it will decompose into OH, monatomic oxygen, monatomic hydrogen, O ...
The exothermic (heat producing) reaction between potassium permanganate (KMnO 4), a strong oxidizing agent, and glycerol (C 3 H 5 (OH) 3), a readily oxidised organic substance, is an example of an experiment sometimes referred to as a "chemical volcano". [7] [8]
The integral heat of dissolution is defined as a process of obtaining a certain amount of solution with a final concentration. The enthalpy change in this process, normalized by the mole number of solute, is evaluated as the molar integral heat of dissolution. Mathematically, the molar integral heat of dissolution is denoted as
One example of deposition is the process by which, in sub-freezing air, water vapour changes directly to ice without first becoming a liquid. This is how frost and hoar frost form on the ground or other surfaces, including leaves. For deposition to occur, thermal energy must be removed from a gas.
Most liquids freeze by crystallization, formation of crystalline solid from the uniform liquid. This is a first-order thermodynamic phase transition, which means that as long as solid and liquid coexist, the temperature of the whole system remains very nearly equal to the melting point due to the slow removal of heat when in contact with air, which is a poor heat conductor.